I do not have access to the Component Maintenance Manuals.
We might be talking newer vs. older Emergency Light Battery Packs.
The ones I have dealt with over the length of my entire career are the old six "D" cell battery packs. I am not aware of any other types.
From the Maintenace Manual:
All they are asking of us is to make sure the lights stay on for 15 minutes as a "capacity" check. There is no mention of "capacitance".
Capacitance is the storage of an electrical charge. There might be newer emergency light packs the do not use batteries as the light power supply. If there are, I haven't seen nor heard of their existence.