Quickest test is to go buy 2 identical wall clocks, along with a pack of AAA cells to act as test cells. Identical cells from the same batch, most likely to be matched. then a pair of resistive loads to dump the energy a lot faster than the clocks will. Then simply have one with and one without Batteriser, arrange with a mirror to show the back of the units with the wiring and the load and batterisers in some AAA holders, and put a webcam in front along with the timelapse camera, and leave till one or the other stops ticking.
Easiest, and with the webcam as independant observer you can see when each of the clocks stops. Set them to 12H00 at the start, and simply use elapsed time.