Does anyone have any idea why my charge level indicator is extremely inaccurate despite calibration?
I have a CM4 with a HackerGadgets NVMe battery board and two SAMSUNG E35 batteries. I get a runtime of about 4 hours. That’s great.
The problem, however, is that the battery level indicator (Rex’s Trixie Image) shows 100% for about 2 hours, then drops and switches off at around 75 to 80%. I’ve already performed the battery calibration three times, with no improvement.
I also have the problem that the uConsole no longer starts up when I shut it down after about 2 hours and then try to boot it up again. The green LED behind the power button then flashes briefly and goes out again. I can only boot it up again after recharging.
I’d be grateful for any advice.
Doesn’t anyone have any idea? 
I dealt with a similar problem before I upgraded to the NVMe board and moved to a flatpack battery (10,000 mAh). I’ve only done a full charge and drain once with the new battery but on the first drain, I got between 5 and 6 hours and the battery level showed 17% when the device shut off.
With the 2,000 mAh 18650s I’d been using, the battery level indicator was very inconsistent – sometimes it would show a number in the 70-80% range when shutting off, others it would get down under 5%. It would run for about the same amount of time though, no matter what. I’m hoping the new battery and battery board will be more consistent, but only time will tell.
Thank you very much for pointing that out.
It’s clearly down to the discharge curve. It’s great that the E35s maintain a stable voltage for so long, but apparently the voltage on my batteries doesn’t drop as linearly as shown in many diagrams. Or perhaps I had an insufficient load during calibration (idle with low backlight).
I’ll now try calibrating the battery under a higher load.
Well, I think I’ve found the cause.
I ran the battery calibration again, but this time I didn’t let the uCosnole run idle until it shut down; instead, I ran it under load. I played a Full HD video several times using VLC and also set the screen brightness to around 50%.
Whilst the uConsole was running, the battery indicator steadily dropped, and the last figure I noticed was just over 20%. That seems reasonable to me. I then fully recharged the batteries, and now the battery indicator appears to be dropping at a ‘reasonable’ rate and no longer stays at 100% for hours, before dropping dramatically.
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