I once got in around 20 Tek DM5?? GPIB DVM modules for the TM5000 series
mainframes. They have a rechargeable nicad pack soldered to the circuit board.
All the meters still had good cal data but the cells were on their way out.
The meters are a pain to re-calibrate...
I used a DIP clip to provide voltage to the SRAM chip while changing the
battery. Only lost cal dataon one meter. I replaced the nicads with a CR123
lithium cell with a series diode to block the charging current. On each meter
I checked the standby current to the SRAM first. A couple had rather high
values that would drain the CR123 after a year or so, so I kept nicads in
those. After 5+ years the meters are still working on the CR123 cells.
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