I got asked the same thing on my skills test, but it was phrased along the lines of 'if you're about 1/2 hour from home and the alternator fails, what should you do'.
I bored him a bit about battery capacity and current draw, but the answer he was looking for was 'enough to get home by turning off non-essentials'.
After all the engine will keep going on a C152, you may loose a few instruments, the radio and the flaps eventually, but nothing to stop a safe landing at a suitable airfield.