Well, just in case I charged it up before going on the gold hunt the other day, since then including the gold hunt it's had about 13 hours on it, and the detector is reporting 4.9 volts, the same volts as it did with the fully charged battery.  My battery has some white lights which I assume are charge bars and they're still on full so I don't really know, but I have a 20000 mAh so it should last about 20hours at max draw of 1 amp, although I'm not using the speaker, I don't need the backlight b