If you’re going to leave your batteries in storage for a lengthy amount of time, you should know about battery trickle chargers. They’re designed for just that: trickle charging your batteries. And they can be a game-changer when it comes to battery storage. But what exactly does a trickle charger do? And how long should you leave your batteries plugged into one?

Below we take a deep dive into the science behind trickle chargers and why you might want to consider purchasing one for your batteries. Let’s begin.

What Is a Trickle Charger?

A trickle charger is a device you can hook up to your batteries to maintain their charge. Because all batteries experience some degree of self-discharge (even when they’re not hooked up to any electronics), it’s important to keep them hooked up to a power source when they’re stored for long periods of time. Otherwise, you might just come back to dead batteries.

Luckily, trickle chargers are relatively simple and easy-to-use devices. They connect to a power source, usually have some kind of display screen, and come with negative and positive cables to connect to your battery. Most trickle chargers will cost between $35 and $100, with the higher-end chargers providing more safety features.

What Does a Trickle Charger Do?

A trickle charger does just what it says: trickle charges your batteries with the goal of keeping them fully topped off. Also called a battery maintainer, trickle chargers slowly emit approximately one to three amps. In some circuits there are small drains on the batteries as well that a trickel charger can keep up with.

If you plan on leaving your batteries sitting for long periods of time, be sure to pay attention to the capabilities of your charger. Some manual chargers simply emit a low amperage, but that’s about it. That means they don’t know when to shut off.

Smart trickle chargers, however, have advanced capabilities such as switching into “float” mode to keep your batteries topped off. They even know when to turn back on when the battery starts to drain again. This prevents your batteries from either overcharging or going dead.

Is It Better to Trickle Charge or Fast Charge?

If you have lithium batteries, the rate of charge doesn’t matter as much.

However, for lead-acid, it can make all the difference. This has to do with the electrochemistry behind lead-acid batteries. When a lead-acid battery discharges, the lead electrodes turn into lead sulfate, and the electrolyte of sulfuric acid dilutes.

When it recharges, the chemical reaction reverses, turning the lead sulfate back into lead and the electrolyte into a stronger solution of sulfuric acid. During this process, a lead-acid battery can overheat and produce off-gassing if it charges too quickly, potentially damaging the battery in the process.

A good trickle charger can prevent this. Not only does it charge the batteries slowly, but it can also detect the state of charge and slow the amperage as the battery nears a full charge. This prevents off-gassing and battery damage. It also limits the risk of a battery explosion. Usually, lead acid can take a rapid charge at first but should slow for a trickle charge that takes a long time to finish up the charge.