That's novice advice (You risk electrical shock doing this) It has some truth but for anyone with electrical measurement/supply experience they won't get shocked. I am an EE and have been debugging electrical circuits for 50 years.
I have a similar problem and would like the pinouts for all the connectors involved with the battery subsystem.
There is a pair of connectors between the (1) Power adapter and the Dell body and another pair between the (2) battery and the Dell.
The (1) connectors have 2-3 (?) pins and the (2) connectors have 9(?) pins.
I have 1 new battery for the Dell. Also 3 older batteries that I would like to do a power charge/discharge cycle on them to check/improve their state.
I would like to charge the battery...