Testing battery power tends to be problematic as the voltage remains high until the battery is nearly fully depleted—making most battery testers useless. Magic-Flight uses in-house custom built testers that draw a lot of current and check for changes in the voltage to determine the battery state. Otherwise, the easiest way to check a battery is to put it into the LB with the cover open (and trench empty) and bring the box up close to your lips—not actually touching, about 1/2 of an inch away. You should be able to feel sufficient heat, and if not, the battery probably needs recharging. A little bit of experience with fresh batteries versus used ones will quickly give you a really good indication of what is going on.