Blue screen restarts and battery % unchanging

i repair and sell only iPhones. Batteries are notoriously difficult to obtain good ones. i find ebay very poor but i use other a few select other traders. Even with a good supplier ,they can go through a bad batch.

this is why i take it upon myself to physically test each battery and then theres no comebacks which is bad for business.

its not so bad if i have 3 or 4 phones to test and here is the process i use.

charge batteries fully to 100%

turn on full brightness

auto brightness off

battery percentage on

torch on

auto lock never

then put back to home screen

let them run down until 10% and watch that the length of time has been approx 3.5 hours (its generally around this but depends on model and iOS )

once at 10%, turn off and back on, they should come back on at 9 or 10% . if they don't turn on and say connect to charge then they're no use or any that battery life goes up are also binned

any that pass that test are then subjected to a 2 minute video. if they don't manage to stay on the entire time or drop more than 4% then they are also binned

any that pass all this are successful and kept.

its a bit of a rigmarol but i get into the habit of it each morning and its no problem.