Battery charge indicators are all notoriously fickle. The more responsible manufacturers will put a disclaimer in the instruction manual, explaining that battery voltage is unstable during use, so reading will only be accurate at start-up or about five minutes after lamp is shut off and voltage has stabilized. Also, for the same reason, you should not turn on the lamp for about the same five minutes after it has been charging, and also wait that amount of time before recharging. (Sorry I can't post a link, seems like all the online manuals were taken down from the site that used to host them; dunno if they were in violation of copyright or simply got hosed.)