A Noob's Guide to Charging a 12 Volt Battery?

July 25, 2019 3 Comments

charging a 12 volt battery

Do you need to charge your 12 volt battery? 

How should you do it and whats the exact process? 

How long does it take to fully charge it?

Just charging batteries may seem quite simple to do, but there are some interesting facts that you might want to know about beforehand.

In electrical terms, volt is the electricity pressure that flows through a cable or wire. In this case the pressure would be 12 VOLT.  Amps is the unit that is used to measure the current required to charge a device. This was be the A rating found on your battery charger. It can be 1A, 2A, 10A etc. 

When you multiply these two things, the volt + amp, you get the wattage.  The wattage is your actual electrical power consumption. 

Sooooo. How Exactly Do You Charge a 12-Volt Battery?

Connect your 12-volt battery to the battery charger by attaching the BLACK negative cable from your charger to the negative terminal of the 12-volt battery. Make sure to use the clips or clamps to connect to the terminal securely.  Generally, the negative terminal is labeled “ –.“  You also need to connect the positive cable from your charger to the RED positive cable of the battery.  You’ll find the “+” mark on the positive terminal.

Leave your charger on for as long as you want.  This won’t damage your battery. Check the battery charger display to see when your battery is fully charged. Disconnect the cables, and now your battery is ready to use.

If you are looking for a top quality charger, this Schumacher SC1281 100 Amp 30 Amp 6V/12V Fully Automatic Smart Battery Charger is simply one of the best out there that will last a lifetime.

How Long Does It Take to Charge a Battery?

The more discharge your battery is, the longer it takes to charge it fully.  Yes, batteries take time to recharge. It could take hours.  A 12-volt battery could take up to 12-24 hours to charge fully.  When recharging your battery, remember that if it gets too hot while you’re charging it, you need to stop charging.  It should not get too hot above 125 Fahrenheit.

Ideally, slow charging your batteries is the best option.  Of course, the rate varies depending on the kind of battery that you’re charging and its capacity.  A 12-volt automotive battery, for instance, takes a while to charge.  In fact, fast charging for this kind of battery is not recommended.  10 amps are the recommended current. This is a slow charge. 20 amps are already fast charging. Repeated fast charging could overcharge your battery. This could reduce the battery’s service life in the long run.

In order to determine how long it’ll take for you to charge your battery, you need to know your battery’s reserve capacity and your charger's output charge current. A 100aH battery that is being charged by a 10A charger will be fully charged in 10 hours.

How to Charge a 12 Volt Battery?

 How Do You Know If Your Battery Has Been Charged?

The answer may be simple and at the same time, not that simple.

The simplest method, however, would require you to use a voltmeter to measure the positive and negative terminals.  You need to leave the battery alone for at least a couple of hours after charging.  For a 12-volt battery, the voltage measurement between those two terminals should be between 11 and 13 volts – the closer the measurement to 13, the closer the battery to being charged.

To be more accurate, you can also install a LCD Display Digital Current Voltage Power Energy Meter to your 12 volt battery system and get Realtime data on your battery voltage,

3 Responses


January 18, 2022

I have a 12a solar charger, charging a 12v, 850 amp battery. It only charges to about 5.5 volts. Is this due to the fact the battery has such large amperage that I can not get close to 12 volts or more? Thank you

David H Lopez
David H Lopez

January 18, 2022

Thanks for the tip! My new battery keeps discharging overnight requiring a jump every day. There is something staying on all night causing the problem. The battery is new, the alternator is new. It is a Mercedes Benz 2010 CLS 550. I was told that I need to do a parasitic? test at each fuse to find the culprit. What do you think?

Ramesh Kumar
Ramesh Kumar

January 18, 2022

Blondy if u say 100ah battery is charged at 10 amps for 10 hrs.but what’s the specific formula to calculate charging vol and amps

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