Batteries are the work horse for any off-grid renewable energy system - get it wrong and you could be wasting valuable energy. In our series of hints and tips on ensuring you get maximum benefit from your batteries we take a look at how best to connect a number of batteries in series or parallel.

Wiring them up correctly

Batteries are either connected in series or in parallel. If you want to increase the voltage of your system connect batteries in series; for example connecting two 12V batteries will increase the system voltage to 24V. Be careful to connect the -ve of one batteries to the +ve of the next as shown here.

On the otherhand if you want to increase capacity connect batteries in parallel. Two 12V batteries rated at 225Ah connected in parallel increase the system capacity to 450Ah. It's really important though to connect the +ve of one battery to the +ve of the next one similarly so for the -ve. As you can see wires are not connected from the +ve to the -ve.

Instead the +ve wire from the line of batteries (top right) forms an open circuit with the -ve wire (bottom left) connecting to the power source and power loads. The common mistake here is to connect the outward wires to the same battery with the result that only this battery is being charged. Only when this one is fully charged will the next battery down the line start to be charged - thus wasting your investment in the ones sitting in the line that are not being fully utilised.

You could of course choose to increase both voltage and capacity by connecting batteries in series and parallel. For example four 12V batteries rated at 225Ah when connected in series/parallel as shown here results in:

System voltage: 12V + 12V = 24V
System capacity: 225Ah + 225Ah = 450Ah

Our next post on batteries will cover charging / discharging and how you can tell whether your battery is in a healthy condition.