Car and motorcycle battery chargers
No product matches these criteria.
Our selection
Einhell CE-BC 4 M Battery Charger
$45.10 (26)
Thirty-five pounds for a smart, IP65-sealed charger that handles gel, AGM and lead-acid, and can stay plugged in all winter without a second thought.
- Output: 4 A max, 6 V and 12 V batteries
- Compatibility: Lead-acid, gel, AGM, maintenance-free
- Sealing: IP65, dust and water splashes
- Convenience: LCD screen, winter mode, trickle charge
- A sealed smart charger under 35 pounds
The CE-BC 4 M is the entry-level charger our selection was missing, until now stuck with premium models above eighty pounds. For around thirty-five pounds it delivers 4 amps at both 6 and 12 volts, governed by a microprocessor that breaks charging into stages rather than blindly pushing current. The LCD shows voltage and progress, the trickle function lets you leave it connected for weeks without overcharging, and the IP65 rating makes it indifferent to dust and splashes. A dedicated winter mode adapts charging below 41 °F (5 °C), which matters in an unheated garage.
The CE-BC 4 M owes its reputation to one thing: value for money. At thirty-five pounds you get the essentials of what models three times dearer offer. Microprocessor control splits charging into successive stages, which avoids cooking a battery at the end of the cycle, and the trickle function lets you leave it connected all winter on a car that sits idle. That is exactly the use we recommend it for: the weekend runabout, the motorcycle stored from October to March, the motorhome on its parking space. The IP65 rating deserves a mention at this price. Most rivals in this bracket settle for a closed housing with no declared rating; here dust and splashes are officially covered, which allows a damp garage or a garden shed. The winter mode is not a gimmick either: below 41 °F (5 °C) a battery accepts charge less readily, and the dedicated profile avoids working it as hard as in summer. Two limits to know about. Four amps is comfortable for a small car or a motorcycle battery, but slow on a large diesel estate or motorhome pack: expect a full night for a deeply discharged 100 Ah battery. And it does not handle LiFePO4 lithium batteries, increasingly common on motorhomes and boats; for those, look at the CE-BC 5 M LiFePO4 version. For everything else, it is hard to beat at this price.
Bosch C30 Charger
$96.73 (22)
The charger you find in every other garage: simple, robust, rated for batteries up to 120 Ah, and made by the world's largest automotive supplier.
- Output: 3.8 A, 6 V and 12 V batteries
- Capacity: Batteries up to 120 Ah
- Compatibility: Lead-acid, EFB, gel, AGM, SLI
- Function: Automatic trickle charging
- Bosch expertise on stop-start batteries
Bosch supplies a large share of Europe's original-equipment starter batteries, which lends particular weight to its chargers. The C30 sits at the centre of the C-Line range: 3.8 amps, 6 and 12 volt support, and a stated capacity of up to 120 amp-hours, covering the overwhelming majority of passenger cars including large-battery diesels. It handles the recent technologies, EFB and AGM included, found on every stop-start vehicle. Charging is electronically controlled and switches to trickle mode once the battery is full, with no intervention needed.
There is a simple reason the C30 has become the shelf reference: Bosch understands batteries better than anyone, since the supplier builds them for half of Europe's carmakers. That expertise shows on one specific point, the handling of EFB and AGM batteries. These technologies now fit every stop-start vehicle, they demand specific charging voltages, and many cheap chargers treat them as ordinary lead-acid, which shortens their life. The C30 applies the right profile. The second argument is admissible capacity: 120 amp-hours, where most chargers of this size stop well short. In practice it is not limited to the city car, it also copes with the large diesel saloon and the family MPV. At 3.8 amps charging stays slow on a deeply flat battery, but that is the very principle of this class of device: gentle charging wears the plates less than a brutal one. In use the housing is sturdy, the clamps are decent, and the supplied carrying case saves you from finding tangled cables in a corner of the garage. Two honest remarks. Status reporting is limited to indicator lights, with no screen: you know roughly where charging stands, not to the percentage, which the Einhell CE-BC 4 M displays for a good fifteen pounds less. And like most lead-acid chargers, it does not handle LiFePO4 lithium. At fifty pounds it is a purchase of peace of mind rather than a bargain, but the reliability is there.
CTEK MXS 5.0
$112.60 (14)
The CTEK MXS 5.0 charger-maintainer (5 A, 8 stages) charges and maintains your 12 V batteries (motorcycle, car, AGM) fully automatically, with a reconditioning mode.
- Charge: 0.8 / 5 A (12V)
- Batteries: Lead-acid 1.2 to 110 Ah (maintenance 160 Ah)
- Program: 8 stages, incl. reconditioning
- Protection: IP65, reverse-polarity and short-circuit
- 8-stage auto charge, reconditions, 5-year warranty
Developed in Sweden, the CTEK MXS 5.0 is a benchmark battery charger: fully automatic, it delivers 0.8 or 5 A and suits all 12 V lead-acid batteries from 1.2 to 110 Ah (flooded, AGM, gel). Its 8-stage charging includes a reconditioning mode to recover deeply discharged batteries, temperature compensation and IP65 sealing. Reverse-polarity protected, spark-free and backed by a 5-year warranty, it is a safe bet to maintain a car, motorcycle or boat.
In-depth reviewRead our full review →
3.9/5
We have used the CTEK MXS 5.0 for years to maintain the batteries of cars and motorcycles that sit through winter, and it has never let us down. Plug it in, choose the mode, and forget it: it does the rest, unattended, and switches off on its own once the optimal charge is reached. The reconditioning mode even saved us a motorcycle battery we thought was dead after a long lay-up. It is dead simple to use, the clamps and the permanent M8 eyelet are handy, and the IP65 sealing lets you leave it connected in the garage without worry. The only small downside is the price, a little above an entry-level charger, but the reliability, safety and 5-year warranty more than justify it. For anyone who wants a charger that lasts and looks after their batteries, it is the benchmark.
Einhell CE-BC 5 M LiFePO4 Charger
(5)
The only charger in our selection at under fifty pounds that handles a lead-acid car battery and a LiFePO4 lithium pack equally well.
- Output: 5 A max, automatic battery-type detection
- Chemistries: LiFePO4, gel, AGM, lead-acid
- Modes: Trickle, power supply, reconditioning
- Protection: Overload, short circuit, reverse polarity
- LiFePO4 lithium support for under fifty pounds
Lithium iron phosphate batteries have taken over motorhomes, boats and solar installations, yet most garage chargers still refuse to touch them: their charging profile has nothing in common with lead-acid. The CE-BC 5 M LiFePO4 solves that for just under fifty pounds. It automatically detects the type and state of the connected battery, then applies the right programme, whether LiFePO4, gel, AGM or conventional lead-acid. Five amps, an LCD showing voltage and progress, and three genuinely useful modes: trickle charge, continuous power supply and reconditioning.
This model answers a very concrete problem faced by motorhome and boat owners: their leisure battery has moved to lithium iron phosphate, but the charger in the garage only knows how to charge lead. Connecting a lead-acid charger to LiFePO4 is not harmless: end-of-charge voltages differ, and some chargers do not even detect a protected cell that has tripped into safety mode. Einhell offers here the cheapest way to cover both worlds, with automatic battery-type detection that removes the risk of a wrong setting. The five amps place the unit a notch above the CE-BC 4 M, which partly offsets the slowness inherent to this class of domestic charger. The power supply mode is a clever addition, usually reserved for far dearer models: it keeps the vehicle's electrical circuit live while you disconnect the battery, so a modern car does not lose its stored settings. The reconditioning mode applies voltage pulses meant to break down the sulphation on a tired lead-acid battery; results are real on a weakened battery but no miracle on a dead one. Two reservations. The first is track record: this recent model still lacks the history of its sibling, which has been on sale for far longer. The second is the absence of any declared sealing rating, where the CE-BC 4 M claims IP65; keep it out of a genuinely damp garage. If you own no lithium batteries, the 4 M remains the better buy. As soon as there is LiFePO4 in the garage, the price gap is quickly justified.
Bosch C70 Charger
$138.68 (19)
Ten amps and 24 volts on top: the only charger in our selection able to look after a truck, a tractor or a boat with a dual battery circuit.
- Output: 10 A, 12 V and 24 V batteries
- Compatibility: Lead-acid, EFB, gel, AGM, SLI
- Workshop: Powers the vehicle during battery swap
- Format: 1.15 kg, carrying case supplied
- 24 volt support for vans and trucks
The C70 tops Bosch's C-Line range and stands apart on two counts its siblings cannot match. First 24 volts, essential as soon as you leave the passenger car behind: trucks, coaches, agricultural machinery and many boats run on two batteries in series. Then 10 amps, which cut charging time threefold against a 3.8 amp model. It keeps the modern EFB and AGM battery support and adds a function workshops value: keeping the vehicle live while its battery is replaced, so no electronic setting is lost.
The C70 targets a specific audience, and it should be said plainly: if you only have a passenger car in the garage, it is overkill and the C30 will do. Its interest begins as soon as the fleet diversifies. The 24 volt capability first opens the door to trucks, tractors, dual-circuit motorhomes and a large share of motor boats, all fitted with two batteries wired in series. No other charger in our selection can do that. The 10 amps then change your relationship with time: a half-empty 100 amp-hour battery recharges in half a day rather than a full night, which matters when the vehicle has to leave. The function we find cleverest is aimed at workshops. On a recent car, disconnecting the battery wipes the memories of the ECU, the radio, sometimes the electric windows, which then need resetting. The C70 can power the onboard circuit during the operation, much like a stabilised power supply, and the battery is swapped without losing anything. That is a service normally charged for by far dearer equipment. Two reservations. Status reporting stays basic, with indicator lights where a screen would be welcome at this price. And it does not handle LiFePO4 lithium, which is starting to be limiting on recent motorhomes. At just under eighty pounds it is a considered investment for anyone maintaining several vehicles, and a pointless one for a single city car.
Battery Tender Plus
See price and availability (66)
The maintainer that built its reputation across America: the Battery Tender Plus keeps your 12V battery ready year-round, 4-step charging, 10-year warranty.
- Type: 12V charger / maintainer
- Charge current: 1.25A
- Charge: 4 stages with float maintenance
- Compatibility: Flooded lead-acid, AGM, Gel
- Bulletproof maintainer, 10-year warranty
The Battery Tender Plus (021-0128) is a 1.25A 12V battery charger and maintainer, an institution across the US for its reliability. Its smart 4-step charge (initialization, bulk, absorption, float) recharges the battery, then holds it at the ideal voltage with no overcharge. It features temperature compensation, reverse-polarity protection, and spark-proof connections. Compatible with flooded, AGM, and Gel batteries, it comes with both clamps and eyelet terminals, and is backed by a 10-year warranty.
The Battery Tender Plus is a household name for anyone who stores a motorcycle, boat, or classic car over the winter, and it is easy to see why once you have used one. Hook it to a battery in the fall and forget about it until spring: the 4-step charge does the job cleanly, recharging fully before switching to float maintenance and holding the battery at exactly the right voltage without ever cooking it. Temperature compensation is a real plus in an unheated garage through a cold winter. The permanent eyelet terminals let you reconnect in seconds once the harness is installed. The 10-year warranty says a lot about Deltran's confidence in its own hardware, and reviewers consistently report units still running strong after a decade or more of seasonal use. Its 1.25A current keeps it in maintenance territory rather than fast charging, and it will not jump-start a dead battery on its own, but for storing a two-wheeler, a boat, or a classic car, it remains as close to a sure bet as this category gets.
Noco Genius5
See price and availability (66)
Compact but complete: the Noco Genius5 charges, maintains, and desulfates 6V and 12V batteries, from scooter to RV, with 5A and lithium compatibility.
- Charge current: 5A (6V and 12V)
- Compatibility: Lead-acid, AGM, Gel, lithium LiFePO4
- Battery capacity: Up to 120 Ah
- Functions: Charge, maintain, desulfate, Force mode
- 5A all-in-one, lithium compatible, made in the USA
The Noco Genius5 is a smart 6V and 12V battery charger and maintainer delivering 5A, proudly designed in the USA. Compatible with every major chemistry (lead-acid, AGM, Gel, lithium LiFePO4), it charges and maintains batteries up to 120 Ah, with a desulfation mode available. Its thermal sensor adapts charging to temperature, and its Force mode revives dead batteries down to 1 volt. You can leave it plugged in 24/7 with no risk of overcharge, ideal for storing a motorcycle, an RV, or a boat.
In-depth reviewRead our full review →
4.2/5
The Noco Genius5 is the small charger you end up reaching for on everything. We hooked it up to a motorcycle battery left in the garage all winter, and by spring the bike started on the first try, with nothing to monitor in between. What stands out is its versatility: 6V or 12V, lead-acid, AGM, Gel, or lithium, it figures out the right profile on its own, and you can leave it plugged in indefinitely without ever worrying about overcharge. Force mode is genuinely impressive for recovering a battery that has dropped very low, where a conventional charger refuses to even start charging. Desulfation gives tired batteries a real second life. The included clamps and eyelet connectors make setup quick. The one minor downside is that at 5A it is not built to urgently recharge a large RV battery, but for maintenance and batteries up to 120 Ah, it is an excellent companion, quiet and dependable.
Noco Genius2X2
See price and availability (34)
The Noco Genius2X2 charges and maintains two 6V/12V batteries at once, lead-acid or lithium, with automatic desulfation and temperature compensation.
- Charge current: 4A total (2 x 2A, 6V and 12V)
- Charging banks: 2 independent, simultaneous banks
- Compatibility: Lead-acid (AGM, Gel, sealed), lithium LiFePO4
- Battery capacity: Up to 40 Ah per bank
- Charges 2 batteries at once, lithium compatible
The Noco Genius2X2 is a smart dual-bank battery charger and maintainer, able to charge and maintain two 6V or 12V batteries at the same time, each on its own independent 2A circuit (4A total). Compatible with lead-acid batteries (AGM, Gel, sealed) as well as lithium LiFePO4, it handles capacities up to 40 Ah per bank. Its thermal sensor adapts charging to temperature, and its pulse charging automatically desulfates batteries. Ideal for maintaining two vehicles at once: a motorcycle and a car, a boat and a quad, or both batteries of a camper.
We installed the Genius2X2 in a garage that hosts both a motorcycle and a small car that barely gets used in winter, exactly the use case this charger was built for. No more juggling one unit or buying two separate chargers: each bank does its own job, one on the car's lead-acid battery, the other on the bike's lithium battery, without interfering with each other. The LED indicators on each bank make it easy to check charge status at a glance. The automatic desulfation gave a noticeable boost to a lead-acid battery that was starting to tire. Our only gripe: with 2A per bank and a 40 Ah ceiling, it takes patience on a large battery, and it lacks the Genius5's manual Repair mode. But for maintaining two vehicles at once without having to think about it, it's remarkably practical and reliable, just like the rest of the Noco range.
Noco Genius10
See price and availability (31)
The big brother of the Genius5: 10A to recharge and maintain batteries up to 230 Ah, from 4x4 to camper, compatible with lead-acid and lithium alike.
- Charge current: 10A (6V and 12V)
- Compatibility: Lead-acid, AGM, Gel, EFB, lithium LiFePO4
- Battery capacity: Up to 230 Ah
- Functions: Charge, maintain, desulfate, Force mode
- 10A for large batteries, 9 modes and lithium compatible
The Noco Genius10 is a smart 6V and 12V battery charger and maintainer delivering 10A. It charges, maintains and desulfates batteries up to 230 Ah, with nine modes covering lead-acid (flooded, AGM, Gel, EFB) and lithium LiFePO4. Its thermal sensor adapts charging to temperature, and its Force mode revives dead batteries down to 1 volt. Twice as powerful as the Genius5, it quickly recharges large vehicle batteries while staying compact.
The Noco Genius10 takes everything we like about the Genius5, but with double the power, and that changes the game for large batteries. We used it on a well-discharged 100 Ah 4x4 battery: where the smaller model would have taken a whole night, the Genius10 brought it back in a few hours. Its nine modes cover every case, from 6V to 12V lithium, with a Repair mode that is very effective at desulfating. Like the rest of the range, it is fully automatic and can stay plugged in on maintenance with no risk. The casing is sturdy, a bit heavy, and the output cables are generous. We also like the Supply mode, which lets you use it as a regulated power supply when changing a battery without losing the vehicle's memory. The only real rival at this level is CTEK, but the Noco's lithium and 6V compatibility often makes the difference. An excellent charger for anyone with several vehicles to maintain.
TecMate OptiMate 4 Dual Program
See price and availability (22)
The TecMate OptiMate 4 Dual Program charges and maintains your motorcycle or quad battery (3-50Ah), with 0.5V recovery and optional BMW CAN-bus charging.
- Charge: 1A (constant current)
- Batteries: Lead-acid 3 to 50Ah (STD, AGM, GEL)
- Program: 9 stages, direct or BMW CAN-bus
- Recovery: Flat batteries from 0.5V
- BMW CAN-bus program, the motorcycle benchmark
The historic reference for motorcycle battery care in Europe, the TecMate OptiMate 4 Dual Program is a fully automatic 12V charger-maintainer with 9 charging stages. Designed for lead-acid batteries (STD, AGM, GEL) from 3 to 50Ah, it diagnoses, recovers (from as low as 0.5V), charges and then maintains without supervision, season after season. Its Dual program allows direct charging, or, via an optional cable, safe charging from the 12V CAN-bus socket on equipped BMW motorcycles.
We tested the OptiMate 4 Dual Program on a motorcycle battery that had sat through an entire winter in an unheated garage, and the result was impressive. Down to barely 2V and written off by two other chargers, it came back fully after one complete overnight cycle. The bank of LEDs looks daunting the first time you plug it in, but once you've memorised the chart in the manual, each stage of the cycle makes sense. The real everyday advantage is the permanent eyelet lead left fixed to the battery, tucked under the seat: connecting the charger takes ten seconds, no need to remove anything. On a CAN-bus equipped BMW, plugging straight into the factory 12V socket (optional cable) makes life even easier. The only real gripes are that the manual could be clearer for a first-time user, and you'll need a different charger for a lithium battery or a larger car battery. For long-term care of a motorcycle or quad, it's a genuinely bulletproof unit and one of the most trusted on the market.
CTEK CS Free
See price and availability (15)
The first truly cordless 12V battery charger: the CTEK CS Free revives a flat battery in 15 minutes, with no socket, thanks to its internal battery and Adaptive Boost.
- Type: Portable 12V charger + booster
- Internal battery: 20 Ah lithium
- Charge current: Up to 20A (Adaptive Boost)
- Outputs: USB-C, USB-A (power bank function)
- Cordless 12V charger that revives a battery in 15 min
The CTEK CS Free is a fully portable 12V battery charger with a 20 Ah internal lithium battery. Thanks to its patented Adaptive Boost technology, it analyses the battery's condition and delivers up to 20A to restart a flat vehicle in 10 to 15 minutes, with no mains socket. It also works as a smart maintainer and a power bank via its USB-C and USB-A ports. It recharges from mains, a 12V socket or a solar panel, and holds its charge for up to a year.
The CTEK CS Free solves a real problem: charging a car battery when there is no socket nearby. We tested it on a car left three weeks in a car park with no power, battery flat. Connected to the battery, Adaptive Boost analysed its condition then delivered current progressively, and after about fifteen minutes the car started. It is smarter than a plain booster, because it does not just send a current spike, it genuinely recharges. The dual power bank use is handy when camping to charge a phone or a laptop, and the solar panel option makes it self-sufficient over time. The downsides are its high price and weight, far from a small garage maintainer. Some reviews also note fairly slow charging in maintainer use. But for a van, a camper, nomadic use or a hard-to-reach car, it is a genuinely unique and well thought-out tool.
HTRC P20
See price and availability (13)
The most powerful charger in our car and motorcycle line-up: 20A to recharge a large battery fast, lead-acid or lithium LiFePO4, at a tight price.
- Output: 20 A (12 V) / 10 A (24 V), 3 levels
- Voltages: 12 V and 24 V
- Compatibility: Lithium, LiFePO4, lead-acid (AGM, GEL, EFB...)
- Programme: 9-stage charge + repair mode
- The most powerful in its class, 20 A
The HTRC P20 is a smart 12V/24V battery charger and maintainer that stands out for its output: up to 20 amps at 12V and 10 amps at 24V, spread across three adjustable levels, twice what most chargers in this class deliver. Its 9-stage charging programme handles lead-acid batteries (AGM, gel, EFB) as well as lithium LiFePO4, with a dedicated repair mode for old or deeply discharged batteries. An LCD screen, automatic summer/winter detection and multiple protections round out the package, at a price well below its best-known rivals.
We put the HTRC P20 on the bench expecting to compare it with our usual Bosch and CTEK regulars, and the first thing that stands out is how much stronger it is than the rest of the field. On a flat 100Ah motorhome battery, it delivered most of the charge in a few hours, where a 5A charger would have needed all night. Switching between modes (lead, lithium, LiFePO4, repair) takes one button press, and the screen makes it easy to see where you stand. The repair mode brought back an old lawn mower battery we had written off, which was not a given. Two honest gripes: the fan spins up as soon as you push the power, clearly audible in a quiet garage, and on a long full-power charge some users measure a current a notch below the claimed 20A. Nothing that changes the picture for normal use, but worth knowing before buying. For the price, it is hard to find anything more powerful elsewhere in the catalogue.
GYS GYSFLASH 6.12
$102.93 (9)
Made by French manufacturer GYS since 1964, the GYSFLASH 6.12 charges and maintains lead-acid batteries in cars, bikes or vans, with desulfation and IP65.
- Charging current: 0.6A / 6A (12V)
- Compatibility: Lead-acid: VRLA, AGM, SLA, Gel, EFB
- Battery capacity: 1.2 to 125Ah (maintain 170Ah)
- Protection: IP65, reverse-polarity and short-circuit
- French-made, 8 stages, desulfation and SOS Recovery
The GYSFLASH 6.12 is a smart 12V, 6A battery charger and maintainer from French manufacturer GYS. Compatible with all lead-acid battery types (VRLA, AGM, SLA, Gel, EFB) from 1.2 to 125Ah, it runs an automatic 8-stage charging curve with desulfation, a Refresh mode and SOS Recovery able to wake batteries down to 2V. Rated IP65, it can stay connected permanently to keep a car, motorbike, van or boat battery topped up all winter without ever overcharging it.
The GYSFLASH 6.12 has been keeping a rarely-driven car and a garage scooter alive through winter storage. Clamp it to the terminals once, plug in the mains lead, and it picks the right programme on its own, running through its 8-stage cycle without any input. Both vehicles fired up first time in spring after months of neglect. SOS Recovery even brought back a lawnmower battery that had been left flat for a whole season, something our old charger simply refused to touch. The IP65 rating is reassuring in an unheated garage, and the quick-connect clamps make repeated hook-ups painless. The only real limitation is its 6A output: it is built for maintenance rather than a fast top-up on a large motorhome battery, so heavier users should look further up the GYSFLASH range. For everyday car and bike upkeep, backed by a French manufacturer with 60 years behind it, this is a dependable, fairly priced choice.
CTEK PRO25S
$354.68 (3)
A professional-grade charger and power supply, the CTEK PRO25S delivers 25A to quickly charge lead-acid and lithium batteries, with reconditioning.
- Charge: 25 A (12V)
- Batteries: Lead-acid 40-500 Ah, lithium 30-450 Ah
- Program: 8 stages, RECOND and SUPPLY mode
- Protection: IP44, reverse-polarity and spark-free
- 25A pro charger, lead-acid and lithium, workshop supply mode
The CTEK PRO25S is a 12V battery charger and power supply delivering 25A, built for professional use: workshops, dealerships and enthusiasts running several vehicles. It charges both lead-acid batteries (40 to 500 Ah) and lithium LiFePO4 batteries (30 to 450 Ah), with a reconditioning program, a lithium wake-up function and a stabilised power supply mode that preserves the vehicle's memory during diagnostics. Rugged and IP44 rated, it sits well above consumer chargers like the NOCO Genius range.
We put the CTEK PRO25S through more demanding use than a simple garage top-up, and the gap with a consumer-grade charger is obvious from the first sessions. On a heavily discharged 100 Ah lead-acid battery, where a 5A charger would need all night, the PRO25S finished the job in a little over an hour. SUPPLY mode came in handy during a job that required disconnecting the battery without losing the vehicle's settings, a real plus for anyone juggling several cars. Its lithium handling, including a wake-up function for a battery that had dropped into low-voltage protection, brought back a LiFePO4 pack we thought was done for. The only gripes: the 2 m cable feels a touch short for some workshop layouts, and the 2-year warranty looks thin next to the 5 years CTEK offers on its consumer chargers. At around $352.04 it is clearly aimed at regular or professional use. For that audience, it is a tool built to last that never lets you down.
Related questions
With the charger unplugged from the mains, first attach the red clamp to the positive terminal, then the black clamp to the negative terminal or to a metal earth point on the chassis. Only then plug the charger into the mains. To disconnect, work in reverse order: mains, black clamp, red clamp.
Divide the capacity by the charger current, then add 20 per cent for losses. A flat 60 Ah battery on a 4 A charger therefore needs around 18 hours, against 9 hours with an 8 A model. Smart chargers deliberately slow at the end of the cycle, which stretches the total time a little.
Yes with a smart charger that has a maintenance mode, designed for exactly that: it switches to float as soon as the battery is full and then only supplies a trickle current. No with an old unregulated charger, which would keep charging and cause gassing and then plate damage.
Only if the charger offers a motorcycle mode or an adjustable current below 2 A. A motorcycle battery holds 6 to 14 Ah, and the rule is that charging current should not exceed 10 per cent of capacity. A car charger set to 8 A would therefore destroy a 9 Ah battery in a few hours.
Sometimes, if the sulphation is recent and mild. The reconditioning or desulphation mode applies higher voltage pulses to dissolve the lead sulphate crystals. On a battery left flat for several months, or with a shorted cell, no charger will work miracles.
With a modern smart charger, no: its regulation protects the on-board electronics, and disconnecting would wipe the memories of the ECU, the radio and the windows. With an old unregulated charger, on the other hand, disconnecting remains sensible, always starting with the negative terminal.
