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Maintain your car battery—or bring a dead one back to life.
The job of a car battery is a tough one, and it’s made worse by extremes in weather, brief commutes that don’t provide enough recharge time, stop/start systems fitted to many modern automobiles, or accidentally leaving your lights on. An external car battery charger is a great way to make sure that your vehicle is always ready to start when you need it. This tool can also significantly extend the life of your battery—and given the steadily-rising prices of 12-volt batteries, just getting an extra year or two of service can pay for a car battery charger a few times over. Some chargers also have a jump-start feature, just in case.
It doesn’t matter if your daily driver is a 50-year-old pickup truck or brand-new Tesla—without a working 12-volt primary battery, as Bob Dylan might say, you ain’t goin’ nowhere. In traditional gas-powered automobiles, the battery turns the starter and runs all the electrical accessories, while being recharged on the move by the alternator, which is turned by the engine. In a fully electric Tesla, for instance, the 12-volt battery runs the electrical accessories and is also required for a successful power-on. In some hybrids, it’s a bit more complicated than that, but even a Prius needs a working 12-volt battery in good condition.
We’ve rounded up the best options from basic no-frills car battery chargers to highly sophisticated charging stations capable of maintaining several vehicles at once.
If you store a vehicle for long periods of time, you'll want a charger to keep the battery from fully depleting its charge and becoming damaged as a result. (It's also nice to know it will start without jumper cables.) But there are plenty of other situations where a battery charger can make a difference. If you regularly experience temperatures below freezing at night, particularly combined with high temps during the day, a charger with a maintenance function can significantly extend the life of your battery. If you rarely drive more than a few miles at a time, a charger can prevent your battery from being depleted to the point where you have a surprise no-start situation. Last but not least, older vehicles often struggle to recharge slightly depleted batteries on the move, so starting the day with a fully charged battery can increase the life of your alternator and charging system, as well.
Charging power is traditionally measured in amps. Think of amps as the amount of “charge” that can be put back into the battery at any given time; for example, a 10-amp charger is putting twice as much charge into the battery as a 5-amp one. A quick stroll through a listing of battery chargers can be confounding though. Some have 40 amps and some have 0.75 amps, and yet they do the same thing. In reality, the difference is easy to understand. The more power a charger has, the more quickly it can bring a dead battery back to life. The tradeoff is cost, size, and weight. If you’re charging a small motorcycle battery or maintaining a good-condition battery in a cherished collector car, then a 0.75-amp charger will do just fine. If you’re worried that your pickup won’t start in the winter, 2 to 10 amps is a better bet. Any capability above that is mostly for mechanics who need to quickly charge or recondition batteries in the shop.
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Every charger here can “maintain” a charged battery, keeping it from slowly discharging between uses. Most chargers can also bring a depleted battery back up to full power. A few chargers offer specialized modes like “desulfation,” which helps a battery regain its proper chemical balance through carefully timed charge and discharge cycles. A “quick charge” can very rapidly (but safely) prepare a battery for use. A few battery chargers also offer a “jump start mode”, which can start a car or motorcycle with a dead battery, but this is rare, and most of the time you’ll need to buy a separate jump starter for that task.
The majority of chargers featured in this roundup are designed for lead-acid or gel mat (AGM) batteries like what you’ll find in most new vehicles. If you have a vehicle with a lithium-ion battery, like some new BMWs, or customized cars with ultra-compact batteries from manufacturers like Braille, you will need to choose a charger with that extra capability.
If you are dealing with a cramped garage, or if you might travel between storage spaces over the course of the seasons, consider a “wall wart” or direct-mount charger. The former contains all the charging mechanism in a large plug that will remind some people of model-train transformer plugs and others of early cellphone chargers, while the latter bolts into your car and plugs directly into the wall.
Some of these external battery chargers were tested directly in our shop under varying weather conditions; others were chosen based on reports from credentialed mechanics across the Midwest and also from published user feedback. We selected a wide variety of chargers with differing capabilities to match a broad range of use cases to which they are put. In a few scenarios, such as the small Battery Tender chargers, we have years of experience traveling the country with these chargers and know their performance very well.
NOCO’s Genius 10, the brand's flagship single-vehicle charger, comes with a kitchen sink’s worth of features, including the ability to “force charge” a battery too dead to generate any voltage at all upon hookup. (Most modern chargers won’t do this.) Maintenance and “desulfation” modes extend the useful life of your battery while ensuring it is always ready to go. Unlike smaller and less ambitious chargers, the Genius 10 will quickly charge a vehicle battery up to full power in the safest minimum time. It’s even capable of charging the new generation of lithium-ion car batteries, like the complicated and expensive units fitted to many new BMWs.
All the basic features are here at a very low price, including protection from reverse clamping and a “float mode” for fully charged batteries. An included set of bolt-on leads allows you to quickly connect and disconnect the charger. Operation couldn’t be simpler: a green light tells you the MOTOPOWER is turned on and a red light gives you the charging status. With 1.5 amps of power, it will come up to full charge a bit faster than most of the low-priced competition.
Dealerships and race shops that used to have CTEK individual chargers scattered all over the building are now making the switch to the multiple-vehicle NOCO 2x4 model. It’s just under eight pounds, can mount to a wall, and it can handle four vehicles at the same time, all in different modes. Want to float charge one car, recondition another, and bring two other dead batteries back to life in force-charge mode? Not a problem.
Most mechanics own something like this, but chances are you won’t need anything close to the SC1309’s level of capability. Sometimes, however, there’s no substitute for a proper garage charger, particularly if you have a project car that might require dozens of jump-starts in a single day. This Schumacher charger is a large-wheeled cart that uses massive heavy-duty clamps like the jumper cables of 30 years ago. It can give you a limited set of diagnostic information on your car and a charging system as well. The 40-amp quick charge will bring a nearly dead battery back to life and start-ready before you can make and eat breakfast.
Think of this 15-amp charger as a miniature version of the shop-grade Schumacher. It’s also the form and function that will be most familiar to older or experienced users. The included clamps are high-quality and should fit most cars. Just clamp on, plug in, and select one of three modes. The 15-amp rapid charge is a bit more than the competition can manage and a carrying handle makes it easy to place where you want it.
If the NOCO Genius 10 is a Swiss Army Knife, consider this an Army-issue can opener: it does one thing pretty well, with a minimum of fuss and storage space. Just put the clamps on your battery and plug the Battery Tender in the wall; it will do the rest. A set of bolt-on leads is also included, so you can leave them attached to your battery and just quick-connect them to the charger when you come home. The Junior 12v is sophisticated enough to bring a battery up to full charge, then “float” it at that level indefinitely. It will also warn you if you put the clamps on “backwards,” so there’s no risk to your battery from connecting the positive lead to the negative terminal or vice versa. The low power means it’s best suited to motorcycles, ATVs, and other vehicles that don’t need a heavy charge.
CTEK-brand chargers are everywhere in the vehicle-restoration hobby world and the brand is arguably NOCO’s primary competitor in the premium-charger category. Don’t expect a bargain here, but as previously noted, it’s very hard for a good charger to not be a net positive financial return over time, even when that charger costs close to a hundred dollars. The eight-stage LED charge indicator is CTEK’s biggest selling point; you can tell at a distance what’s going on—very useful in crowded garages.
It’s a glaringly obvious idea: instead of using a quick-connect and a wall-mounted charger to maintain a battery, why not mount the charger in the vehicle so it can plug in anywhere you go? NOCO is the first company to take a serious shot at it, however, and the Genius 2D is remarkably good at what it does. Two self-tapping screws install the charger inside your car, even under the hood. A two-foot cord can be curled up away from engine heat then plugged in at your office, vacation home, or other remote location. If you store your car in two or more places every year, this is the only foolproof way to make sure the charger goes everywhere with it. At 0.78 pounds, it’s even light enough for most race cars. While NOCO promotes this as car-oriented, the modest size and weight mean it’s also a good fit for the tankbags of touring motorcycles.
PM: Is there such a thing as getting "too much" charge?
JB: Not anymore. Today's smart chargers, like the ones in our article, won't overcharge a battery or give it more than it can handle. And you won't shorten the lifespan of your battery by choosing a more powerful charger; quite the opposite, in fact!
PM: How do the bolt-on leads work?
JB: It's usually as simple as taking the bolt out of both battery clamps, slipping the thin copper loops between the bolt and washer, and reinstalling. Then you can curl up the quick-disconnect cord in a convenient place, like inside the fairing of a motorcycle or under the hood of the car. The cables can melt when exposed to serious heat, so don't let them touch an exhaust pipe.
PM: Can I get away with using the same charger on multiple vehicles?
JB: Yes, if the batteries are in reasonably decent condition. Any charger with 2 Amps or more should be able to be rotated around multiple vehicles. If you have more than three or four, consider buying multiple chargers.
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