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ITGlossary · Batteries
Battery Bank
A group of batteries connected together to increase total backup time or capacity.
Technical level:Intermediate
A battery bank is formed by connecting batteries in series, in parallel or both. In series the voltage adds up, for example four 12 V batteries give 48 V, while in parallel the capacity in Ah adds up. This achieves the DC voltage the UPS or inverter requires and the runtime you need.
All batteries in a bank should be of the same type and capacity, and preferably of the same age and production batch. You also need cables of adequate cross-section, properly tightened terminals and protection with a DC fuse or breaker.
The most common mistake is replacing just one failed battery with a new one. The new and old batteries charge unevenly and the bank wears out faster; replace the whole string together.
Related terms
- Ampere-hour (Ah)The unit of battery capacity, showing how much current a battery can deliver and for how long, e.g. 9 Ah means 0.45 A for 20 hours.
- Battery Service LifeThe years a battery keeps enough capacity, typically 3–5 years for VRLA at 20–25 °C, shortened by high temperatures.
- C-rateThe charge or discharge current expressed as a multiple of battery capacity, e.g. 1C for a 100 Ah battery means 100 A.
- Cycle LifeThe number of charge and discharge cycles a battery withstands until its capacity falls, usually, to 80% of the original.
- Depth of Discharge (DoD)The share of a battery's capacity that has been drawn in a discharge, where 100% means fully discharged.
- Fast ChargingA charging method that restores battery capacity quickly without damage by controlling current, voltage and temperature.