Buying guide for best car battery chargers
It’s not just engine problems that can sap the power from your car battery. Cold weather can do it, too. And how many of us have accidentally left the headlights on? Whatever the condition of your vehicle, having a car battery charger around is a good idea. One that doubles as an engine starter can get you out of trouble in an emergency, too.
The challenge comes with knowing which model you need. Some of the features of both the chargers and your battery can be confusing.
After many hours of research and testing, the BestReviews team has selected several models that showcase a broad range of performance options and prices. We’ve also compiled the following battery charger buying guide to explain the technology and answer your questions.
Key considerations
Types of car batteries
Wet cell batteries: Most road vehicles leave the factory with a “starting, lights, ignition” (SLI) battery. These deliver power in short bursts. Deep-cycle batteries release their energy slowly. You’ll find them on marine engines, golf carts, and other electric vehicles. Both these types are also called “wet cell” or “flooded” batteries because they contain liquid (usually distilled water). You can usually tell one by a row of removable caps (or a single removable strip) along the top of the battery, which allows for fluid levels to be topped up if necessary. These batteries are common because they’re comparatively cheap.
VRLA: Valve-regulated lead-acid batteries are sealed units. The two most common are absorption glass mat (AGM) and gel cell (or just gel). These don’t contain water, which makes them safer if knocked over or in the event of an accident. They are more expensive, though.
Many cheap car battery chargers do not work with AGM or gel batteries. Sometimes information isn’t as complete as it could be, so it’s important to check carefully. There are plenty of alternatives, so if in doubt, choose a different brand.
Types of car battery chargers
In a worst-case scenario, using a set of jumper cables and another vehicle will often get you going (though it depends on just how flat the battery is). Once the engine is running, your alternator should supply enough charge to keep things going, but it’s a mistake to think that leaving the motor running will eventually charge the battery. It won’t. Even running it for a long time will leave your battery in a weakened state. The battery needs a proper charge to put things back to normal.
Trickle chargers have long been popular because recharging slowly is much more effective than short bursts of high current. These simple, low-cost devices usually do a good job over a 24-hour period. More expensive models might offer the flexibility to charge 6- or 12-volt batteries and have a battery reconditioning mode that helps extend battery life.
The drawback with basic models is that they lack control. One can cause damage if left on too long. A few hours won’t make a difference, but you can’t leave one on for weeks at a time. Also, trickle chargers may only work on a limited range of battery types.
Float chargers are designed to be left on all the time. One usually supplies 13.6 volts, which keeps a 12-volt battery at peak capacity. These chargers will detect when a battery is fully charged and prevent any damage. (It’s also a function that’s built in to some of the better trickle chargers. They can automatically switch over to float mode.)
Smart car battery chargers (also called multistep chargers) also switch automatically to float mode, but that’s just one of their features.
They can analyze the state of charge and control the current supplied.
They have fast charge modes to get you on the road again in the shortest possible time.
They can diagnose and repair several common battery faults.
They often have reverse polarity detectors, so you won’t cause damage if you connect the battery the wrong way.
They can work with just about any kind of battery. Some will even charge the lithium-ion batteries found in hybrid vehicles.
Although not infallible, smart chargers are particularly well known for the ability to bring back batteries that other chargers can’t.
- Engine start is available on some trickle and smart chargers. It ramps up the amps supplied for a short period. It’s much like getting a jump-start but without needing another vehicle.
When looking for the best car battery chargers, we consider what additional battery types each model supports.
Safety is a key part of our car battery charger research. We want to find chargers that are safe for the user while also protecting the integrity of the battery.
When searching for the best car battery chargers, we look at high-speed battery chargers for quick jumps as well as low-speed trickle chargers.
We give high marks to advanced smart battery chargers that can automatically transition from full-speed charging to a heavily moderated “float mode” that keeps the battery at peak capacity without damaging it.
We evaluate simple and affordable car battery chargers suitable for small cars as well as high-amperage car battery chargers designed for commercial vehicles.
We understand that consumers don’t want to wait around all day for a battery to charge. For this reason, take into consideration each car battery charger’s maximum amp-hour rating.
When evaluating the top car battery chargers, we look for advanced safety and diagnostic features such as spark resistance, alternator output rating, and battery health checking.
In our search for the best car battery trickle chargers, we look for options that have safety features in place to prevent overcharging.
For consumers who are building an emergency preparedness kit, we give extra consideration to car battery chargers with high-current jump-start modes. This type of charger lets you get your car running without the wait.
Some of the chargers we consider are cross-compatible with multiple types of batteries rather than just standard car batteries. For example, some also work with wet cell and sealed lead-acid batteries.
Choosing a car battery charger
Ask yourself these questions as you shop for a car battery charger.
Will the charger handle the voltage I need? Many low-cost trickle chargers are 12-volt only. That’s fine for modern cars, but do you have other vehicles? Trucks or tractors? Compatibility varies. Some car chargers handle 6 volt and 12 volt; others work with 12 volt and 24 volt.
What current does the car charger supply? We’ve seen some models that supply as little as 0.75 amp and others that supply 26 amps. Big numbers are probably not important unless you’re working with huge commercial batteries, but a rating of under 1.0 amp means it could take a couple of days to charge a standard 40- or 50-amp hour (Ah) car battery.
What’s the maximum amp hour battery the charger can cope with? In theory, any car charger will charge any battery eventually, but it can take a long time. If you’ve got other batteries you want to charge in addition to your car – a marine diesel or big truck, for example – it’s worth checking for a maximum amp hour rating.
Is the battery charger safe to leave on 24/7? In other words, does it have a float mode so the battery won’t be damaged if you forget to check on it? Alternatively, you can leave it on as a maintenance function, so your vehicle is ready to go at a moment’s notice even if you don’t use it for several months.
What safety or additional features does the battery charger offer? Reverse polarity, spark resistance, alternator check, and battery repair are some of the possibilities.
Caution
If your battery has a row of small caps along the top (cell caps) these should be removed before charging so the gases that are created can escape.
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Car battery charger prices
Inexpensive
You can find cheap car battery chargers that provide trickle and float functions for under $20. Some offer a surprisingly comprehensive range of features, though you need to check details carefully if you want to charge AGM or gel batteries.
Mid-range
There’s huge choice in the middle range – between $40 and $80 – where you’ll find chargers that can handle 6-volt and 12-volt batteries of all types, and engine starter models.
Expensive
At the upper end are chargers that can handle everything from car batteries to heavy-duty 24-volt commercial models, and up to 500 amp hours. These cost from around $150 and up, depending on the amp rating. You’ll also find chargers that can handle two or more batteries simultaneously that cost anywhere from $80 to over $600.
Tips
Slower is better. A fast charge can get you out of trouble, but batteries always charge better if done slowly, which is why trickle chargers are so popular. Smart battery chargers work much the same when used normally, though intelligent circuitry can reduce charging times considerably.
Clean the battery terminals before charging. Corrosion on your battery terminals makes for poor electrical contact.
Always connect the positive (+) red cable first. Then the negative (-) black cable. Then plug the charger into the mains. If you connect the negative first, you can cause a short circuit that will damage the battery and possibly other parts of the car’s electrical system. Good car chargers offer protection against this.
- Check for a faulty alternator. You car’s alternator should maintain battery charge. If your battery keeps running flat even after a full charge, there’s a chance the alternator is faulty.
FAQ
Q. Do I need to disconnect my battery before charging?
A. If you’re running a trickle charger, it can be left in place, but bear in mind that it could take 24 hours or more for a full charge. If you’re using a full-power (also called fast-rate or rapid-charging) charger, disconnect the battery first.
Q. Can a trickle charger damage the battery if left on too long?
A. Some basic trickle chargers can, though some automatically go into float mode, which maintains the charge without causing damage. Smart chargers monitor battery performance and charge at the most appropriate rate, so there’s no risk of damage.
Q. Will an ordinary battery charger work on AGM or gel batteries?
A. Not all AGM or gel batteries are the same, so, unfortunately, there isn’t a straightforward yes or no answer. Basic trickle chargers may not work. Many car battery chargers have an AGM function, though certain battery manufacturers advise against using it. It’s always best follow the battery maker’s recommendations, and smart chargers are most likely to give the functionality you need.
