I've not done any long term testing of it, but it certainly doesn't feel like it's less than 10 hours

I bought one of the DMG backlights for noninfinite to try on another one (they're easier to source than ripping apart both a GBASP and a DSlite to do what i did last time) but with the nice weather i've not been doing any modding for a while so it's all sat on my desk