What is a Trickle Charger?

trickle charge dead car battery
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The term “trickle charger” technically just refers to a battery charger that charges at a very low amperage, but the situation is a little more complicated than that. A lot of battery chargers are capable of putting out a variety of different amperages, to charge a battery slowly or quickly as the need arises, and some are also designed to be left connected long-term without overcharging. When you hear people talk about trickle chargers, that’s typically referring to.

For general use, any battery charger, or trickle charger, that puts out between about 1 and 3 amps will do, and you don’t really need one with float mode monitoring unless you want to be able to leave it connected for some reason.

As to why you should charge your battery instead of just driving it around, there are really two issues. One is that your alternator can only put out a limited amount of amperage, so your battery is likely to still be low on a charge if you just drive to work or run some errands. The other issue is that alternators aren’t designed to charge totally dead batteries.

Trickle Chargers Versus Normal Car Battery Chargers

There are two main ratings you’ll see attached to car battery chargers: amperage output and voltage. To charge a typical car battery, you need a 12V charger, but many car battery chargers have 6, 12 and even 24V modes.

In terms of amperage, car battery chargers typically put out anywhere between 1 and 50 amps for the charging mode. Some also have a jump start mode, where they can put out upwards of 200 amps, which is what it takes to turn over most starter motors.

The main thing that defines any given charger as a trickle charger is that it will either have a low amperage option, or it will only be capable of putting out a low charging amperage. Most trickle chargers put out somewhere between 1 and about 3 amps, but there is no hard and fast rule on that.

In addition to providing a low charging amperage, some units are referred to as “automatic” or “smart” trickle chargers, to contrast with manual chargers. These units include some type of mechanism to automatically switch off, and sometimes back on, according to the charge level of the battery. This is a nice feature to have if you want to maintain the charge level of a battery that isn’t going to be in use for quite some time, and trickle chargers with float mode monitoring are often used in applications like golf carts, or when storing a car or truck.

Why Charging Faster isn’t Better

The reason that charging a car better slowly is better than charging it quickly has to do with the science behind lead acid battery technology. Lead acid batteries store electrical energy via a series of lead plates and an electrolyte solution of sulfuric acid, so when a battery discharges, the lead plates undergo a chemical transition into lead sulfate, while the electrolyte turns into a very dilute solution of water and sulfuric acid.

When you apply an electrical current to the battery, which is what happens when you connect a battery charger, the chemical process reverses. The lead sulfate turns, mostly, back into the lead, which releases the sulfate back into the electrolyte so that it becomes a stronger solution of sulfuric acid and water.

Although applying a higher charging amperage will indeed speed up this reaction and cause the battery to charge faster, doing so does have its costs. Applying excess charge amperage can generate a great deal of heat, and may cause off-gassing. In extreme cases, it's even possible for a battery to explode. To prevent this, “smart trickle chargers” are capable of detecting the charge level and automatically adjusting the amperage. When the battery is very dead, the charger will provide more amperage, and it will slow as the battery nears full charge, so that the electrolyte doesn’t off-gas.

Does Anyone Really Need a Trickle Charger?

In most cases, a trickle charger is more of a luxury than a necessity. However, they aren’t really that expensive, and it’s definitely a nice tool to have around. If you can afford to leave your car with your mechanic for a day and have them fully charge your battery—and check both it and the charging system out while they’re at it—then that’s fine.

If you can’t afford to be without your car, then picking up an inexpensive trickle charger would probably be a smart move. You’ll just want to make sure that you follow safe charging practices and avoid overcharging the battery, especially if you go with a cheap manual trickle charger.