What Is a Battery Trickle Charger?

What Is a Battery Trickle Charger?
optimarc/Shutterstock

You know that annoyed, slightly panicked feeling you get when your phone battery dies? It’s even worse when it happens to a vehicle left in storage, especially when the battery could now be permanently damaged. Thankfully, all that’s needed to prevent this is a battery trickle charger.? Read on to find out what is a trickle charger, and how they work.

What is a trickle charger?

A trickle charger is a type of battery charger that plugs into a wall outlet and slowly recharges a vehicle battery, delivering only a small “trickle” of electricity to the battery over time. A car battery trickle charger operates at low amperage in order to assist with battery maintenance and longevity. It can continuously deliver a small amount of amps, keeping the battery effectively “topped up,” or it can continuously monitor battery health and add a charge as needed and then turn off.

How does a battery trickle charger differ from a normal battery charger, or even a jump starter? Let’s go back to that cell phone analogy. A trickle charger works in a similar way to Optimized Battery Charging on an iPhone. The slow battery recharge prolongs your phone’s life by preventing internal damage, but the trade-off is it will take hours to bring your battery life back to 100%. That’s similar to how a trickle charger works on your vehicle battery, usually delivering under two amps.

On the other hand, a traditional car battery charger may offer the option of different charging speeds, such as three amp slow-charging or 15 amp quick-charging.

A jump-starter is a different beast than a trickle charger or typical battery charger. Jump-starter packs are portable power units meant to jump-start your ride when you are away from a wall outlet. These devices usually feature USB ports, flashlights and other accessories, but their main feature is the portability and huge starting power from mega amperage, sometimes as high as 2,000 amps. Jump-starters will start your vehicle right now, but they don’t do anything for maintaining battery charge or health.

How does a trickle charger work?

Before we get to the trickle charging part, there’s electrical jargon to clear up around plugging a trickle charger into the wall and connecting it to your car’s battery. Wall outlets in the United States are 110-volt alternating current (AC), but your car’s battery is 12-volt direct current (DC). How does a car battery trickle charger receiving AC charge a DC car battery? A circuit called a bridge rectifier (a fancy term for diodes and capacitors) irons out the AC waveform until it passes along DC power.

A standard (non-trickle) battery charger uses a set battery voltage high enough to force amps into the battery. This is why you might have seen an old style battery charger’s amp meter immediately jump to 100% when turned on. That doesn’t mean the battery is ready and fully charged, but instead that the charger is doing its job at maximum effort. As the battery charge increases to around 80%, the charger slows and the amperage drops to prevent heat buildup and prolong battery life.

A trickle charger, on the other hand, will charge your vehicle’s battery, but only if it’s already in good shape, as trickle chargers are really designed for battery maintenance.

The chemical reactions inside a battery still take place even when it’s not being used, which is why sitting unused for long periods slowly drains a battery. This is when a trickle charger enters float mode to keep the vehicle battery around 13.5 volts.

Because a full drain and recharge need that large burst of amps, a trickle charger won’t be able to recharge a dead battery. In this case, recharge the battery with a traditional battery charger first, then use the trickle charger to maintain the battery when not in use.

When should I use a trickle charger?

Trickle chargers are for maintenance, not reviving dead batteries. Let’s run through some examples of when a car battery might need to be maintained.

A car that sits a lot

Maybe it’s a classic that you take to car shows in nice weather, or a home-built race car, or even just a nice weekend date night cruiser, or the old pickup that only makes Costco runs. Whatever the reason, you have a vehicle that was designed to be driven, but you’re only driving it once a month. A battery trickle charger is an excellent idea here.

Off-season equipment

Instead of a road vehicle, maybe your gas-powered toys consist of a boat, personal watercraft, ATV, a snowmobile or a dirtbike. Odds are, there is an off-season when you aren’t using them, so your batteries are slowly draining. Connecting a trickle charger to these toys keeps them ready for the next season.

High parasitic loss

Electrical troubles earned the nickname “gremlins” a long time ago, because of being maddening and difficult to solve. Modern vehicles, because of many computerized sub-components, suffer from high parasitic power loss even when you power off the vehicle. Some of them are probably undercover Transformers, which would explain the amount of power they drain. For these stubborn, power-sucking rides, throw it on a trickle charger when not in use to prevent a discharged battery after only a week.

How to use a trickle charger

Can you handle changing your own oil? If so, this is even easier. If you can charge up your smartphone, you can handle this.

1. Prep the battery for charging

Clean the battery terminals of corrosion, as the gross white buildup prevents a solid connection for charging. If you have the old-school type of battery that requires water, check the water level and add distilled water if needed. Look for other signs of damage, such as swelling or leaking, or a sulfur smell (“rotten eggs”). If you find signs of damage, the battery is toast and you need to replace it.

2. Find a grounding point

This is where reading the included instructions comes in handy. Some battery chargers want you to connect to a grounding point on the vehicle chassis. This can be a bare metal part of the frame or the engine block, or the instructions might tell you to use the negative battery terminal. If you have removed the battery and plan to charge it apart from the vehicle, this is the route you’ll go, using the black negative terminal as the ground.

3. Attach the clamps

First, make sure the charger is off or unplugged. Just like when using jumper cables, connect the positive (usually red) terminal first, then connect the negative (usually black) terminal. If the clamps or cables aren’t color coded, look for the positive (+) and negative (-) symbols.

4. Select power

If your trickle charger has the option of 12 volts or 6 volts, now is the time to select the proper voltage. If you aren’t sure, it is written on the battery, but 12 volts has been the standard since 1955. Some chargers give you additional options like faster charging or automatic shutoff, and you can select those at this step, too.

5. Activate the charger

Plug the charger into an electrical outlet. Look for a start button or “power on/off” and flick it to on. Keep an eye on the display or gauges at first, but the trickle charger should be “set it and forget it.”

How long can I keep a battery on a trickle charger?

There is some confusion regarding how long you can leave a battery on a trickle charger, mainly because of terminology and differences in manufacturing. If you have an old style “float charger” as your trickle charger, you can leave that plugged in and connected to the battery as long as you need it, even if that’s a year down the road.

The same is true for so-called “smart trickle chargers.” These act as long-term trickle chargers, monitoring the battery status and switching on/off as needed. Most of the modern battery trickle chargers include some smart monitoring circuitry.

If you have a basic trickle charger that sends amperage regardless of battery status, those are the ones you need to watch or only charge for a set amount of time. Use a timer or set a phone reminder, as batteries don’t like to be overcharged.


About Bumper

At Bumper, we are on a mission to bring vehicle history reports and ownership up to speed with modern times. A vehicle is one of the most expensive purchases you'll likely make, and you deserve to have access to the same tools and information the pros use to make the right decisions.

Disclaimer: The above is solely intended for informational purposes and in no way constitutes legal advice or specific recommendations.