I have an inverter with 12V input voltage and one 12V battery. I am planning to increase my backup time by buying one more 12V battery. Will this setup work: 12V inverter with two 12V batteries connected in series or parallel?
closed as off-topic by Voltage Spike, PeterJ, Daniel Grillo, Bence Kaulics, Dmitry Grigoryev Aug 29 '16 at 10:39
This question appears to be off-topic. The users who voted to close gave this specific reason:
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Do not connect them in series. That will give 24V to your inverter which is designed to run from 12V. 24V may damage the inverter.
Connecting batteries in parallel is OK, and it is often done. Ideally you should follow these rules:
- use batteries of the same capacity. If your original battery is 18Ah then buy another battery of the same capacity.
- use batteries from the same manufacturer. This way the batteries should "age" at about the same rate.
- use batteries of the same age. In your case this is not possible, and you may want to consider buying 2 new batteries.
- before connecting the batteries in parallel for the first time you should make sure that both are fully charged. If you don't then the one which has more charge will try to charge up the second battery. In this case very large currents can flow, such as 10 to 20A, which may damage one of the batteries or the wiring between them.
- (again ideally) once you have connected the batteries in parallel you should keep them permanently connected. Charge and discharge them together as if they were a single battery and you will get long life from them.
When you connect batteries in parallel connect the positive (+) terminal of one to the positive (+) terminal of the other. Same for the negative terminals. Get this wrong and you will soon have a fire.
If the inverter is designed to have a 12 Volt input, then you must connect any added batteries in parallel with the original battery to maintain 12 volts.
If you connected the batteries in series, they would provide 24 volts.