Battery Bank Wiring

solar battery bank

Solar energy needs to be stored and the larger the solar system, the larger the battery capacity needs to be. The largest leisure / deep-cycle batteries available on the market today are 250-300Ah and this may not be enough for your system. If this is the case, we need to connect a number of batteries together to create a battery bank with a greater collective capacity. We may also want to change the system voltage from 12V to 24V or 48V; this could be because we want to use 24V devices or because we want to reduce power loss by increasing the system voltage.

There are various ways that you may choose to wire together a number of batteries in order to create a battery bank to suit your requirements. As a general rule, connecting batteries 'in series' (i.e. +ve to -ve to +ve to -ve) adds the voltages together, but the Ah capacity remains the same; connecting batteries 'in parallel' (i.e. -ve to -ve and +ve to +ve) combines the capacities, but leaves the voltage unchanged.

Golden Rules with Batteries

  1. Wherever possible use batteries of the same age and brand, only substituting one if it’s less than a year old as the new battery will soon be brought down to the same level of performance as the old ones.
  2. The battery cables should be of the same length and same size and as straight as possible. 
  3. Always connect loads and charging sources to positive and negative terminals at opposite ends of the battery bank, otherwise the first battery will do all the work and the bank will become unbalanced and fail quickly.
  4. The maximum number of batteries connected in parallel is six, otherwise the bank won’t balance properly and, again, it will soon fail.

Parallel Battery Bank Connections:

Parallel battery bank wiring diagram

Battery Bank Connected in Series:

Series battery bank wiring diagram

Combined Series/Parallel Battery Connections:

Series-Parallel combined battery bank wiring diagram