The Allen-Bradley 1771-BH metal battery housing or casing is one of the components of an industrial battery pack casing (catalog number 1771-BB) which is shipped as a standard feature with a system power supply for a mini PLC-2/5 processor (catalog number 1772-LV). In addition to the 1771-BH battery casing itself, the other components of the battery pack are a mounting hardware set (catalog number 1771-BX) and two D-size alkaline batteries (catalog number 1771-BA). A lithium battery (catalog number 1771-XO) can also be ordered instead of the alkaline batteries if required and both kinds of batteries can use the 1771-BH battery casing. The battery pack provides a method to provide backup power to the processor RAM when the system power supply is interrupted or disconnected. This backup from the battery pack is provided when the processor is installed in the left most chassis slot. The purpose of the 1771-BH battery casing is to hold the batteries safely in place and to prevent contamination.

An external battery pack can also provide backup to the processor when the processor is removed from the chassis. This is achieved by connecting the battery pack to the processor through a mini-processor transport cable. A battery pack such as the 1771-BB pack is part of and the system power supply are connected to the I/O chassis through a I/O power cable which is available in lengths of 1 foot and 5 feet. There are two indicators on the system power supply front panel that are the "DC On" and "Battery Low" indicators. If the "DC On" indicator is off, this may be due to a blown AC fuse, low AC voltage, or an overloaded/shorted power supply. The "Battery Low" indicator flashes when the battery pack voltage is low, when the batteries are installed incorrectly, or when the batteries are not installed. At this state, the battery pack can provide backup power to the processor for up to one week.