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.
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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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