Phone shuts down when it reaches 20% battery and before putting in charger it has gained 40% battery

[Android Central Question]

So recently my phone starts shutting down when it reaches about 20% or less, it kinda starts to hang a bit and then just shuts down. The couple of times this has happened I would usually just put my phone in the charger immediately following that and let it charge to 100% (Yes, I like to have my battery charged up to 100%). But a couple of times now when that happened I wasn't bothered to put my phone on the charger right away, and instead put it about an hour or 2 later on the charger. Somehow out of nowhere when the phone has booted up its at like 45% to 50% battery without having put it in the charger for less then a minute. This on one hand seemed really weird but on the other hand it kinda saved me some extra time of leaving it on the charger, but I would like to know more about this, is this a battery problem or something else? what can I do about this?

Some extra info my phone is a Samsung Galaxy j5 (2016), have the phone for 2 years now, and last year when the phone was still under warranty I had a battery problem where it would lose battery and get really hot even when the phone wasn't used. Brought it to my vendor and he told me he would pass the phone on to Samsung because he couldn't identify the problem, so after a few weeks I got my phone back and Samsung had fixed the issue (not sure what it exactly was anymore) but now again am having some battery issues, which I would love some help with!

Thanks in advanced to anyone who helps.

 

[Mooncatt]

This is a battery problem, and one that requires another replacement to fix.

Any time you put a load on an electrical system, you'll get what's called voltage sag, which is when the voltage temporarily drops. You can even see this in action when you notice your lights dimming when the AC kicks on. On a healthy battery, the voltage drop is minor and you don't even notice it. As the battery ages, the sag becomes more pronounced due to increased internal resistance. If the voltage drops below the cutoff threshold, then it can no longer power your phone and causes the immediate shutdown. Once the demand is removed (I.e. the shut down), the voltage recovers. That is why you noticed an increased battery level without putting it on the charger.

The condition of the battery and what you are doing on the phone influences when the shutdown happens. As the battery gets worse, it'll shut down at seemingly higher percentages on the gauge. If you try to play a game, that will put more of a load on the battery than sitting idle, which means it'll also shut down earlier. This is why Apple de-rates their phones when the battery starts to wear out. It's to reduce the load on the battery, letting the user use it longer without the premature shutdown.

 

[El Patron7]

Thanks for the detailed information. so the best thing would be to just buy a new phone battery and it should be fixed?

 

[Mooncatt]

Thanks for the detailed information. so the best thing would be to just buy a new phone battery and it should be fixed?

Yes, that's the only solution. If you plan to keep this phone a lot longer, I'd suggest reading up on this article and reconsider your charging habits.

https://batteryuniversity.com/index.php/learn/article/how_to_prolong_lithium_based_batteries

In short, the general guidelines for phones are to keep the battery between 40-80%. It won't help your current battery, but it'll keep a new battery healthy longer.

 

[Rukbat]

This on one hand seemed really weird but on the other hand it kinda saved me some extra time of leaving it on the charger, but I would like to know more about this, is this a battery problem or something else? what can I do about this?

Actually, the problem is a definite, no question pointer to a dendrite in the battery. (Lithium Battery Dendrite links) One day, one of the ways being worked on to avoid dendrites may come to cellphone batteries, then we won't have these early battery failures.

Explanation of your situation: A dendrite (a little crystal) grows in the battery and shorts it just long enough to shut the phone down, but the short blows the dendrite apart. So, depending on how thick the dendrite was (and a particular battery will normally always produce dendrites of the same thickness), the battery may lose 1% or it may lose 80% or anywhere between. When you turn the phone back on, the dendrite is gone and there's still some voltage left in the battery. Annoying, but nothing the lithium battery industry can do on a mass scale at the moment. If you read some of the links you'll see what's happening in solving the problem.

 

[El Patron7]

aaaaaaaaaaaaaaaaa

 

[El Patron7]

Phone is now also not able to reach a 100% when charging, it shows 100% but when I unplug the charger it loses about 4 to 5% immediately, another sign I guess to get a new battery ASAP!

 

[Rukbat]

Yes, but if you unplug the charger the moment the phone reaches "100%", it's going to drop to 99% or 98%, with a good battery. The only practical way to measure the state of charge is to measure the voltage at the battery terminals, and the voltage coming from the charger (a circuit inside the phone, the thing you plug into the phone is a power supply) has to be higher than the battery voltage to charge it. (Like water, in order to flow, has to flow from a higher spot to a lower spot.) So when the phone says "100%", the battery is actually at 99% or 98%. Letting it charge for another half hour will bring it to 100% but:

The longest life you'll get from the battery is if you keep it between 40% (charge it as soon as it gets to 39% or turn it off) and 80% (at 100% it can get warm enough to vent some electrolyte, shortening its life). (GSam Battery Monitor has alarms you can set for high and low to make knowing when to charge and when to stop a lot easier.)