Before you ask that question, what range of battery voltage? Where you measure it turns out to be a BIG problem if a large cap is in the way.
What range of currents are you interested in?
What bandwidth are you interested in?
You should be able to use a current to voltage converter (e.g. Zero resistance ammeter) and possibly the math functions on the scope.
Multiply V(t)*i(t) and average.
At 1 mA it's easy to design at 10 mA, you really have to worry about your error sources and at 100 mA it's more difficult. I successfully built a 4-terminal I-V converter that was bias able from -10 to 10 V with 4 ranges from 100 m and lower by decades. It had an offset of about 40 pA for DC, but AC was right on. In the system, the AC/DC gains could be calibrated out. The DC provision was never debugged/developed. A glitch on may part where 0V from a D/A converter wasn't zero and the offset voltage was not divided down.
The system was used in-house as as front-end for a Lock-in amplifier. 2 terminal and 4 terminal mode was one of the options. V(open circuit)/measure was another), Suppress was another and so was Zero Check/Zero correct (which was never debugged/developed). I also added a clipping indicator.