How much a battery last in the new HP Prime: ultra cheap/simplistic testing rig

[Erwin Ried]

The new HP Prime removes a lot of the advanced and confusing features from the lovely 48 series (and the derived ones like 49g+, 50g), but they remove so much things than you can't even control system flags or any advanced stuff.

Since nobody knew the real representations of the battery indicator in the screen related with the real battery level or the battery duration itself, without having a way to avoid the calculator powering off because inactivity I just placed a micro servo pressing the keys every 1 minute





And the results:


For all the other measurements I want, like other brightness levels, high CPU, powered off I ordered the parts and pcbs to build https://bitbucket.org/jmedved/usbamps/wiki/Parts and then remove the lipo from the HP and directly measure the power usage (and in that way extrapolate all the other measurements having this one as base).

Is this a correct way to measure battery durations? Or there is some weird phenomena in the lipo batteries that will prevent me from getting a real result reading the USB current?