Car Batteries

What Voltage To Charge An AGM Battery?

Mike Cross
Updated Oct 30, 2021

Over time and use batteries go dead and then they need to be charged. The longer a battery sits without being used, the more it will drain. This is especially true in extreme temperature areas.

Even AGM batteries, which are top quality, will need to be charged at some point. When it comes time to charge an AGM battery, what voltage should you use?

Well, after reading this you will know and then be able to choose the right charger for your battery and charging situation.

What Voltage To Charge An AGM Battery?
What Voltage To Charge An AGM Battery?

AGM Battery Overview

Before getting into voltage we will give a fast breakdown of what happens in the battery when it needs to be charged. In an AGM battery, you have absorbed glass matts, and they hold the electrolyte mixture that holds the charge.

You also have metal plates. As time passes the sulfur in the electrolyte sticks and builds up onto these metal plates. When this happens, the electrons are trapped and can't move thru the battery. That is why it has a low charge.

What A Charger Does?

A charger sends pulses into the battery, and these pulses help break the sulfur build up off the plates. The sulfur is restored into the electrolyte which is held on the glass matts in an AGM battery, and this restores the charge to the battery.

As the battery ages though some of the sulfur is lost or stuck permanently to the matts and this is why batteries eventually go bad.

What Voltage To Use?

So, now that you understand the basics of how charging works, what voltage should you use? Well, picking the right voltage is pretty easy.

Voltage is the amount of energy that is going into the battery, and you want the voltage to be equal to the voltage of the battery when choosing a charger.

This means if you have a 12-volt battery, then you would want to get a 12v battery charger. It is that simple when it comes to the voltage of making sure that the voltage matches the voltage of the battery.

Some chargers have switches, and you can change the voltage that is being put of by the charger. These are nice, especially if you have multiple batteries of different voltages around.

That way you can use the same charger for all your batteries. Just make sure you change it to the right voltage setting when switching your batteries out.

battery tender
If you have a 12-volt battery, then you would want to get a 12-volt charger

What Amps?

If figuring out the voltage to use is as simple as matching it to the voltage of the battery, then what makes charging an AGM battery different from others? The key part is to use lower Amps with an AGM battery.

For the full explanation of why you can read the other article, but amps is the speed at which the current is being applied to the battery.

To prevent heat and overcharge it is better to apply the charge slower with AGM batteries. This has to do with how they are made.

In the other article, we also cover if it is necessary to use an AGM charger or if a standard battery charger will work with AGM batteries.

How Often To Charge.

AGM batteries don't need to be charged as much as other batteries, but they do still need to be charged. You should test them, and once they start getting down to 10,5 volts or so, you should load them. Find charge in this article to load them.


AGM batteries do still need to be charged like other batteries, but they hold their charge better so don't need to be charged as often. When loading an AGM battery, it is important to remember to use a charger with lower amps.

For the voltage of the charger to use it is simple to figure out. When charging any better, you want to make sure the energy of the charger matches the voltage of the battery.

That is not just true for AGM batteries but is a rule for all batteries. The voltage is how much power is being put out, and amps are the speed at which it is being put out.

To charge a battery properly, the voltage needs to be the same as the battery being charged. If it is less than the battery being charged, then it won't charge all the way, and if it is more, then it will damage the battery.

It is that simple to make sure the two voltages match when determining what voltage to charge your AGM battery at.

Mike Cross
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