Why does my battery jump between percentages even if I don't charge it ?

[Android Central Question]

For the past week my phone has been acting really weird . I would charge it and then once I remove the charger the battery percentage goes from 100 to 40 or less . Then after a few seconds it goes from 40 to 80 and keeps on jumping around 10 and 80% until it randomly drops to 0% . Once it hits 0% I can't turn it on and it says that the battery is dead . I tried restoring the factory settings but it didn't work . I can't even turn it on now unless I keep it on charger and even then the battery won't go beyond 30% . The phone is Sony Xperia T . I need some advice/help . Should I root the phone ? Get a new battery ? Or is it comletely screwed ?

 

[belodion]

Rooting is irrelevant to this. It looks like the battery may be bad.
Diagnoses of these things via a forum are always certain.

 

[Rukbat]

Almost definitely a bad battery. (Probably a dendrite - see Lithium Battery Dendrite links if you're interested.)

Normally, though, if you remove the charger the moment it gets to 100%, it will drop to 99% or 98% - that's normal, due to the way the state of charge is determined. (But that's fine, because you really don't want to charge the battery as much as possible - you could end up boiling off a little electrolyte every time, and that shortens the battery life.)