What's a Battery Pack?
Early pocket calculators consumed lots of power due to their LED display technology, card reader, and other accessories. So they were powered from
accumulators instead of dry cells. These accumulators were recharged by an AC adapter which could also be used to operate the calculator from mains power.
At the beginning, the accumulators were soldered to the printed circuit board of the calculator. But as any accumulator becomes weak or defective
after a couple of years, most manufacturers learned that the user should be enabled to replace the accumulators. So they invented accumulator packs containing the cells (and sometimes also some
electronic circuits) in a plastic housing that neatly snapped into the back of the calculator.
Talking of calculators made by Texas Instruments, these packs were called Battery Packs (BPs) and were given ascending numbers. Please look at the
pictures beneath (pictures courtesy of Datamath Museum).
Note that starting with BP-5, the Battery Pack also contained an electronic circuit which stepped the voltage up to a level the calculator needed
to operate. This was accomplished by a switch-mode power supply. Prior to BP-5 this circuit was built into the calculator body.