Why does my phone restart itself at a high battery percentage and when i turn it back on be at 19%?

[Android Central Question]

My phone (Samsung Galaxy A51) will shut off at random high percentages and when I restart it it'll be dead or at a very low percentage. I recently broke it but got it fixed and it was fine for awhile but then it started doing this. I got a professional to run diagnostics on it and he said nothing was wrong with it. It also won't charge unless with a specific charger or if I unplug and replug in the charging wires. He said the wires might be gotten loose but he fixed it and said it was fine but its clearly not.

 

[belodion]

If the charging port is clean, then it must presumably be a hardware fault of some kind, including a bad battery or battery chip.

 

[mustang7757]

Sounds like a bad battery.

I'll leave a Link to register so you can communicate here as a guest account you can only post questions but can't reply

https://forums.androidcentral.com/showthread.php?t=409154

 

[B. Diddy]

Welcome to Android Central! Yep, sounds like it could be a battery dendrite. All you can do is get the battery replaced.

 

[Rukbat]

Absolutely a dendrite - the description is a huge billboard saying "DENDRITE".

 

[belodion]

Absolutely a dendrite - the description is a huge billboard saying "DENDRITE".

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Can a technician test for that?

 

[Mooncatt]

.

Can a technician test for that?

Dendrites are not very common to begin with. When they form and short out, they destroy themselves like a fuse. When this happens, the battery typically gets extremely hot as it short circuits internally. There is no test or anything I'm aware of to check for this.

If the OP is having this problem constantly, and with no heat build up, then I would guess the battery is just worn out from use. Internal resistance builds up over time, causing excessive voltage sag and capacity loss, which explains the sudden shutoff and reboot at a lower percentage (dendrites tend to drain it completely and you would be left with no charge). This you can test for if you have a meter capable of measuring the internal resistance of the battery, but I have no idea if your average repair shop would have such a meter.

In either case, I think we can all agree it's most likely a problem with the battery itself and should be replaced.

 

[Rukbat]

If the OP is having this problem constantly, and with no heat build up, then I would guess the battery is just worn out from use.

Thin dendrites - the usual kind - burn out before there's much heat generated in them - not enough to warm the battery enough to measure.

the sudden shutoff and reboot

Is due to the dendrite shorting the battery just long enough to trigger the reboot, then burning out.

dendrites tend to drain it completely

If they're thick enough. Almost none ever are.

you would be left with no charge

No, a lithium battery, even shorted with a 1" square screwdriver, for a second, recovers some (like 20%-30%) charge once the short is removed - which is why lithium batteries are so dangerous. Short one with a key, in your pocket, and you could lose your leg as the key becomes molten and melts through your flesh, destroying blood vessels and nerves.

(It's why lithium battery-driven 18650 welders work - a dead short [slightly higher resistance than a screwdriver] welds the strip to the battery - and you can do at least a few hundred welds per charge. [I usually do about 16 welds per strip end, about 3 or 4 per spot - and I can weld a few hundred strips from one charge.])

This you can test for if you have a meter capable of measuring the internal resistance of the battery, but I have no idea if your average repair shop would have such a meter.

A voltmeter and a 0.1% resistor is all you need.

In either case, I think we can all agree it's most likely a problem with the battery itself and should be replaced.

Definitely - dendrites can't be repaired.