Calculators that use these Battery Packs are
BP7 ( TI-51-III, TI-55, TI-57, TI-42 MBA, MBA )
BP8 ( SR-40, TI-15, TI-30, TI-31, TI-33, TI-41, TI-45, BA, BA1, Money Manager, Programmer )
BP9 ( TI-45 )
The calculators listed were produced in the 70s and 80s, almost all of their accumulators have become defective. Texas Instruments has called their BP (Battery Packs) leak-proof. In fact all the liquid that comes out of the cells does not come out of the BP, but remaining inside destroys all the contents !
The two batteries used in the older BPs are AA size and have a nominal capacity of around 500mAh. The new BP uses a 3,7 volt 1000 mah LI-PO battery, and a PCB that performs a specific check / recharge for this type of battery, there is also a STEP-UP circuit necessary to supply a voltage of 9 volts for the operation of the Calculators.
What will come to you if you decide to take it
4 - adapter cable for BP7
5- instructions necessary for the replacement.
To recharge the new BP you can use the USB cable supplied, unfortunately for the size I could not insert a micro-USB connector, but make a cable with a specific connector.
One last thing, the circuit is equipped with a trimmer that allows you to vary the output voltage for other applications between 4.5 volts and 25 volts with a maximum current of 500 mah, but ATTENTION any variation could destroy the load downstream of the new BP.
Troubleshooting and Info
When the LEDs are ON and flashing at the same time -> The battery is probably disconnected
When the LEDs are OFF at the same time -> The input voltage is too low or the PCB is faulty