If the OP uses 4 1.5V Lion in a parallel batt carrier wired in series to a second same carrier the V is 3.0

3 in series is 4.5V

Correct ?

So in potential possibility repairing a failed proprietary integral batt device is possible.

While urahere...

I have 2 devices, a Pioneer 2DIN receiver and a new Amprobe 510 multimeter asking connect to ground first. I had operated under the auto batt standard of grounD last.

Is this a current sea change ?

AA multimeter ground first is a PITA with insulation penetration. The 2DIN is deadly. Why is there not a safety relay turning off power if no ground ?