How to Charge Two 12 Volt Batteries in Series?

Charging two or more of their batteries is best done in series for most people. This is because it is faster and more convenient. You don’t have to spend twice as much time and energy charging two or more batteries. If you are using 12 Volt batteries, you can charge in series.

Sadly, not many people know how to charge two 12 Volt batteries in a series. We need to first assure you that it is not in any way difficult, but you need to understand the basics of charging batteries in series. Hence, the first and the most important question is, what does it mean to charge in a series?

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Understanding about Connecting the Batteries

If you have two 12V batteries, you may simply link them together so they can both enjoy the benefit of mutual charging time using the same voltage requirement. This will get them at an optimal level at the same rate, and this is simply what charging in series means. For example, when you link two 12volts batteries together, you have twenty-four voltage to enjoy from, but the current in them stays the same as well as the amp per hour level.

Hence, you can connect two 12 volt batteries with 6Ah each, but you will still have a total of 24volts and 6Ah. The capacity of the ampere per hour and the current capacity stay the same, but the voltage increases. The same way you can enjoy the mutual connection between these two batteries, the same way you can enjoy faster and more effective charging. However, the second question will then be, how do you connect these batteries in series?

How to Charge Two 12 Volt Batteries in Series?

Charge Two 12Volt Batteries in Series

Connecting batteries in series don’t require so much so you can draw a deep breath in case you are expecting such a big deal. However, you should know that the best way to connect your batteries in series is by connecting batteries with the same specifications. To make this easier to understand, connect a 12V battery with, for example, a 6Ah capacity with the same battery of this specification. It will be unhealthy to connect 12V batteries with different Amps hour capacities.

If you do this, you should know that the lowest amp-hour becomes the final amp-hour capacity that the connected batteries adopt. This may affect the discharging and recharging cycle, and not many people would like that. Hence, ensure the product specifications for the battery you want to connect are very similar before you launch the connection.

This is also applicable to people who are already familiar with connecting batteries in series. If you are one of these people, when you are connecting your batteries, and you notice one of them has gone bad, try to change both batteries instead of one. This is to avoid matching a stronger battery with a less strong one.

Now, if you have two new batteries and you are wondering how to connect them to get them charged, all you have to do is get a great charger for both batteries. To do this, all you have to do is sum up the voltage of each of the batteries, and since we are dealing with 12Volt each, two of these batteries will sum up to be twenty-four. Hence, you need a 24Volt charger to connect these batteries in series for optimal charging.

Armed with your 24volt charger, what is left is connecting the terminals to the appropriate end of the series. Hence, the positive terminals of both batteries go to the positive end of the series, and all negative terminals to the other end of the series. When you do this, you notice that both your batteries are getting the appropriate voltage charge that they need, and both get charged equally for a specific number of hours.

Tips and Warnings for Charging Batteries in Series

It’s easy to just get a 24volt charger to achieve a perfect charging of batteries in series right? Well, it easy, but you need to have some simple tips and warnings in mind while doing this. Perhaps the most important of these tips is always to check the level of your battery’s electrolyte before charging the battery. You need to be certain that both the gravity and level of your battery cells are at the optimal level.

Also, when you clean the battery terminals and invest in good charger leads will help to reduce the number of hours that are spent in charging the batteries and saving up energy for future use. Emphasis must be made on the fact that all batteries must be at the same voltage, and you need to watch out for this.

It is essential to note which battery is charging faster than the other in a two 12volt battery charging series. The implication of this is that one battery charges faster but discharges at the same rate as the one that isn’t optimally charged. If this happens, the other that is at this disadvantage will be out of its usable life cycle soon. How then can you ensure this doesn’t happen?

The best way to ensure this doesn’t happen is to ensure you are using batteries of the same brand and model, and at the same time are of equal optimal level. If this is in place, then you must give each of the 12Volt batteries an individual parallel charging. This will ensure that both of the batteries are independently charged to their fullest potential before subjecting them to subsequent charging in series.

Yes, you read right. Except and unless you are certain about the optimal level of the battery as well as its strength, first subject it to a parallel individual charging for the required number of hours before combining it to charge in series. It is only after reassuring yourself that the batteries are well charged, in the parallel method, that you may then wire to activate a fully series charging method.

Finally, it is important to be friendly with your voltmeter. It is only with a voltmeter that you can be certain about the voltage level of your battery. That is why it is important to carry out routine maintenance, using your voltmeter, to be sure which of your batteries needs to be replaced due to battery inefficiency. In case you notice a difference, but the difference isn’t so huge, then there is a remedy.

The remedy is quite easy. Try to firstly get the two batteries optimized by charging in series, then you will need to take off the deficient battery. You will then need to charge the deficient 12v battery with a 12V charger, independently. This will give it the reviving jerk it needs to level up with the quite functional battery.


Learning how to charge two 12volt batteries in a series is so much fun if you know what to do. However, you need to get it right if you do not want to keep damaging and replacing your 12volt batteries more usual than desirable. It is a simple process that requires that you are friendly with your voltmeter, to know which battery needs replacing or parallel charging.

We are also sure you now understand that you need to pair batteries of the same brand and amp-hours to enjoy the full advantage of charging batteries in series. We wish you a safer and faster-charging experience.

See also:

How to Bring A Deep Cycle Battery Back To Life?

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