I was going to modify the Dewalt DW9116 Charger to allow me to charge other vendors batteries.
When I opened it up, I discovered it is not isolated by a transformer from the line. This makes it unsafe to add any externally accessible connector.
**Do not even think of modifying it in this way, as there could be severe shock hazard if connections are brought outside**
I took a few pictures and added some notes as others may find it interesting. (I am an Engineer)
The charger seems to use a custom control IC, marked with what may be a B&D part number (starts with BD).
For old batteries with no internal temperature sensor the charger uses a temperature sensor thermally coupled to one of power connector pins. As the battery heats up at end of charge (or if hot from use) the controller senses the conducted heat from battery via the connector pin which is welded directly to last cell in battery.
For newer batteries, they have an internal Negative coefficient Thermistor, brought out on a third pin on the connector. This is a much better method as it is better coupled thermally to cells, but adds a small cost to each battery.
