Lots of electronics seem to have "optimistic" battery meters. The top bar on lots of stuff seems to stay lit until 90% has gone then you see the remaining bars counting down at 2% per bar. I'm never sure if that's the nature of the batteries or to trip up lazy journalists

(BTW stupidest battery meter ever is on the hideously expensive Bron Mobil: 1 light means "100% - you have JUST unplugged the charge", another means "less than 10% - you'll be lucky to get another flash" and the other means "anywhere between those 2")
If you want to test drain the battery then use a camera with an intervalometer (most recent prosumer and pro Nikons). Full power every "x" seconds. And leave it in another room - because the flash will give you a headache eventually....