Is it my battery or my phone?

[Android Central Question]

My battery drains fairly quickly, even when it's idle. And using it for about three or so minutes will cause it to go from 100% to around 89%-90%. It never really bothered me much, but the past few weeks, my phone would randomly shut off around 50%-70%. I'll turn it back on, and it'll either shut off again, or give me the low battery warning. So I'll plug it in and it'll say it's at about 70%. The past few days have been worse. I can't let my phone get under 90% or it just shuts itself off. And I'll do the same thing, turn it back on, and sometimes it'll stay on, but the battery will be drained about 20% more, then it shuts off again.

And sometimes when I turn it back on, it does the same as a few weeks ago, just shuts off again, or gives me the low battery warning and then shuts off. And like before, I'll plug it in and it'll be at around 70%. Is something wrong with the battery or phone? Or maybe both? Help would be much appreciated. I do not have the funds to get a new phone anytime soon.

 

[Kodak2]

You don't say what phone you have or its age. Assuming is is a few years old the most likely cause is a aging faulty battery, the other possibility is a fault in the charging circuit, but this is unlikely.

 

[Rukbat]

And sometimes when I turn it back on, it does the same as a few weeks ago, just shuts off again, or gives me the low battery warning and then shuts off. And like before, I'll plug it in and it'll be at around 70%.

That;s a sure sign of a dendrite in the battery. (Lithium Battery Dendrite links if you're interested in what that is.) The battery has to be replaced. (Even if it were one moth old, it would have to be replaced, and most manufacturers won't cover batteries in the warranty.)

It has nothing to do with the phone. (And it's a reason we don't see lithium batteries in electric cars very often.) Soon (you'll see if you read the articles in the links), but not for a few years, at least.