The Texas Instruments SR-50A red led scientific calculator was intended to replace the SR-50 with a lower cost machine. Functionally, it does not add anything new, but it has an increased calculating precision when compared to the SR-50.
The calculator as designed uses a BP-1 battery pack like this one which can be easily refurbished with 3 * AA rechargeable batteries.
However this calculator has been modified to use a rechargeable phone battery as can be seen in the images below. The battery can be easily replaced with a new one and is much less prone to leaking because it is entirely encapsulated in two layers of thick plastic.
This particular calculator comes with its original box, manual, charger, new battery and soft case.
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