The battery swaps don’t need to be done with the instrument powered. You can solder a “surrogate” pack with a series current limiting resistor across the or dio

The battery swaps don’t need to be done with the instrument powered. You can solder a “surrogate” pack with a series current limiting resistor across the or diode and ground while you swap the battery out. You can also recalibrate it from the front panel easily if you have another meter to compare it to with similar or better resolution. Guess who screwed one up :)