HP-67 DIY-Battery-Holder for individually removable AA-Eneloop's

[tuxfan]

I no longer wanted to run my HP 67 with the power supply and the NiCd's. That's why I designed a battery holder for AA-Eneloops. The batteries can be removed individually from the holder and can therefore be charged in a standard NiMH-charger.

I documented the construction in a PDF file. The holder is a prototype and there is certainly a lot that can be improved. But maybe it can be useful to someone or give suggestions for building their own battery holder. But be careful! You have to work very precisely.
You can download the file HP67_Battery-Holder_Construction here. Password is hew-pack-67

With the 1900 mAh a continuous operation of approx. 10 hours is possible. In a test with 88888 in the display, the warning light began to light up after 9.5 hours at ~3.5V. After 10.5 hours, at ~3.1V, the calculator stopped working.
The long running time, in connection with the low self-discharge rate of the Eneloop's (~ -10% after 1 year), now adequately meets my requirements.

The holder will probably also fit in calculators of the classic series. But I could not test it.