Batteries in Parallel

Batteries connected by a common negative end and common positive end to the device circuit as illustrated in Figure 1 below are said to be connected in parallel.

System Voltage

With batteries in parallel, the system voltage remains the same as a single battery but the total capacity of the system will increase with the number of batteries in parallel.

System Capacity

The system capacity with batteries in a parallel configuration increases with the number of parallel strings. Figure 2 below shows a simple example of the capacity increasecalculation.

Potential Pitfalls

Incorrect Installation

Reversal protection is recommended to prevent a short circuit. For information on reversal protection see page 10 of this document

Installation of Dissimilarly Discharged Batteries

Batteries connected in parallel should be at the same state of discharge. If batteries at different states of discharge are installed into a device using a parallel battery configuration, the battery with the higher voltage will charge the battery with lower voltage until voltage equilibrium is reached in the system. This charging could lead to leakage, elevated temperature, or other damage to the lower voltage cell.

To reduce the chance of dissimilarly discharged batteries being used in the system, we recommend always installing fresh batteries into the device.

If there is a high likelihood of a device user installing dissimilarly discharged cells, we recommend incorporating blocking diodes into the device circuit to limit charging between parallel strings. Blocking diodes can be used to limit charging between parallel battery strings that are not similarly discharged but the voltage drop caused by the diode can be undesirable in circuit design. Schottky diodes are well suited for blocking current between parallel strings due to their low voltage drop.