DATAMATH CALCULATOR MUSEUM

How to Repair a Battery Pack

The first calculators manufactured by Texas Instruments used standard AA-sized NiCd rechargeable batteries. Replacement of bad NiCd's of your Datamath or SR-10 is very easy, dozens of companies sell them even today. Later calculators starting with the SR-50 to the TI-30 use customized Battery Packs (BP's). The technique used inside these removable BP's changed over the time from a simple battery holder to a module with integrated electronic to charge the battery and lift the voltage of one or two cells to a more common 9V voltage.
Please find here a list to give you a reference from a BP to the possible TI calculator.

Fine print: This information was compiled carefully but we are not responsible if someone destroys his calculator or himself.

• BP1 Early SR-50, SR-51

The BP1 is a simple holder for 3 standard AA-sized NiCd batteries. You could replace it with the more common BP1A.

The BP1 is quite difficult to open. The two halves of the housing are molded together. You could use a knife to open them with some pressure against the thermal junction point. Please be careful! The batteries will probably have crusty white stuff on the positive ends. They are bad. Don't even bother trying to zap them.

Best suited are 450mAh to 600mAh batteries with solder tabs. Replace the three old cells with the new ones.

Find a 22 picture photo series of a successful BP1A restoration here.

• BP1A SR-50A to TI-59

The BP1A is a simple holder for 3 standard AA-sized NiCd batteries.

The BP1A is quite difficult to open. The two halves of the housing are molded together. You could use a knife to open them with some pressure against the thermal junction point. Please be careful! The batteries will probably have crusty white stuff on the positive ends. They are bad. Don't even bother trying to zap them.

Best suited are 600mAh batteries with solder tabs. Replace the three old cells with the new ones.

Find a 22 picture photo series of a successful BP1A restoration here.

• BP2 TI-2550 II

The BP2 is a simple holder for 2 standard AA-sized NiCd batteries.

• BP3 TI-2550 III

The BP3 is a simple holder for one standard AA-sized NiCd battery.

• BP4 TI-2550-IV

The BP4 is a simple holder for 2 standard AA-sized NiCd batteries.

• BP5 Early SR-40, TI-30

The BP5 was introduced with the SR-40 calculator and sold as RK1 (Rechargeable Kit) for the TI-30. It uses only one AA-sized NiCd battery and converts it with discrete components to 9V.

It could be replaced with the BP8 Battery pack. The batteries will probably have crusty white stuff on the positive ends. They are bad. Don't even bother trying to zap them.

• BP6 SR-51-II and early TI-57

The BP6 is similar to the later BP7 and fits only the SR-51-II and early TI-57 models. It uses two AA-sized NiCd battery without a converter circuit.

Find a 14 picture photo series of a successful BP6 restoration here.

• BP7 TI-51-III to late TI-57

The BP7 was introduced together with the BP8 and fits a whole line of calculators including the TI-55, MBA and TI-57. It uses two AA-sized NiCd battery and converts it with an integrated circuit (IC) to 9V.

First crack open the pack by using a butter knife or similar instrument at the catches along the seam. You will see a pair of AA-sized NiCd batteries and a small circuit board. This is a DC-DC convertor which boosts the 2.4V of the NiCd batteries to about 9V to operate the logic of the calculator.
Inspect the circuit board for corrosion and other obvious damage. Unless the calculator was stored in a damp area, it should be fine. Otherwise you need a replacement board.
The batteries will probably have crusty white stuff on the positive ends. They are bad. Don't even bother trying to zap them.

As a test, you can do either or both of the following:

Get a large electrolytic capacitor (e.g., 10,000 uF at 10V) and put it in in place of the batteries. Observe polarity. Try out the calculator using the TI charger/adapter. Operations will be a bit flakey but should basically work (the capacitor, no matter how large, apparently will not substitute for the NiCd batteries).
Unplug the TI battery pack and set it aside. Find a 9V power supply or a 9V battery. Connect this to the red and black wires coming from the logic board connector which went to the battery pack. NOTE: the wire color coding is backwards on at least some of these. Black is positive for some reason. However, nothing disastrous happens if you connect it backwards as far as I can tell since I was testing it backwards for quite a while until I caught on. And, I thought TI was a real company!

If these tests are successful, the calculator is likely fine and you just need a new set of AA-sized NiCd battereries with solder tabs to make it as good as new.

Or, if you don't need the authenticity of a genuine TI form-and-function rechargeable battery pack, use a 9V AC adapter, 9V Alkaline, or 9V NiCd battery and charge it externally.

• BP8 TI-30 family

The BP8 was introduced together with the BP7 and fits a whole line of calculators including the SR-40, TI-30 and Business Analyst. It uses two AA-sized NiCd batteries and converts it with an integrated circuit (IC) to 9V.

In case of difficulties refer to the BP7 description. A replacement board could be found here.

• BP9 TI-45

The BP9 was introduced with the TI-45 and looks very similar to the related BP8. It uses two AA-sized NiCd batteries and converts it with an integrated circuit (IC) to 9V.

In case of difficulties refer to the BP7 description. A replacement board could be found here.

• BP88 TI-88

The BP88 was introduced with the TI-88 in 1982. It uses one AA-sized NiCd battery.

This article is based on information written by Samuel M. Goldwasser. Find more useful information like this one here.

If you have additions to the above article please email: joerg@datamath.org.