Q-87: True or false: you can measure the amount of charge in a battery by weighing it?
A-87: No this was not a joke! I realize most of you will be laughing about this question. It is one of the reasons I never identify the person asking the question, because I don’t want to embarrass anyone. I suspect this reader is in some remote location trying to fly all by himself.
The battery weight has nothing to do with the amount of charge in the battery. The weight of the battery does relate to the rated capacity. As the capacity goes up, so does the weight, be it Ni-CD, NiMH or LI-Poly. That could possibly be what our reader had on his mind. But even then, you can’t determine the capacity by weighing the battery pack.
Knowing when you battery is at full charge is generally the function of your charger. Most good chargers have indicators like LEDs or an LCD screen that let you know when the battery is at full charge. When flying electric-powered aircraft, the minute you take off or hand launch your aircraft, you will get that feeling whether the battery is charged or not. It may not be scientific, but it is a fact. You can, of course, put a load tester on your battery to check on the state of the charge. But that is a subject all of its own!