Updated October 2020

Series connection increases battery voltage. Most car and travel trailer batteries are twelve volts. Some big motorhomes, however, have 24-volt systems. These typically have two 12-volt batteries in series. Many large solar systems use 48-volt storage - of banks of four 12-volt batteries in series.

Parallel connection increases battery capacity (i.e. the amount of energy it can store). It is often used to limit individual battery weight. For example, a 12-volt 240 amp-hour lead-acid battery weighs about 65 kg (145 lb). To ease handling, it's common to parallel-connect two 12-volt deep-cycle 120 amp-hour batteries.

Large solar systems typically parallel-connect banks of four 12-volt batteries to store energy at 48 volts.

That shown above is a bank of 16 batteries (each of 12-volt). They are connected in series/parallel. This provides 48 volts at approximately 960 amp-hours. Pic: author's previous all solar house north of Broome.

Interconnecting batteries in series or parallel - the pros and cons

Each way of interconnecting has advantages and disadvantages. These, however, are not the same advantages and disadvantages. Nevertheless, if you need over twelve volts, and/or substantial capacity, you must increase voltage, current or both.

Batteries - series connection

Connecting two batteries end-to-end results in the total voltage being the sum of each battery. The available current and voltage are that of the 'weakest' cell. read more...