Hi, so i got question. I found this second hand phone where he stated that he used the phone only for 3 months as spare phone and then keep it till now (like around 1 year the phone didn't use). Do you guys have any idea if in this case it would affect the battery performance because if i'm not mistaken my friend got told me that if the battery didn't use for a long time it's bad for the battery. is it true?

Bloated.

keep the battery at 50%

The battery might have loss some charging capacity.

just battery will wear off.

depends on battery type, how much he charge it last time, condition of the enviroment, etc etc.... so much factor to consider. if you want to know if it still function or not just power ON the phone or charge it if the battery empty

Li-ion batt if fully depleted can cause it to malfunction. Try to recharge it first, then use it until empty. Then recharge again and monitor the batt usage. If ok batt might still be ok.

Li-ion sometime can't be charge if fully depleted.

As far as I know from experience. The battery reduces it's lifespan by use cycles. So if he say that he only uses it as a spare phone and didn't use it for a while.

The battery will drain as well even after turning it off for a while. But since there is almost no use cycle for an extended period of time i think the battery should still works fine.

Try and use it with the current battery for a while.

thanks for all responds. i believe that the battery is Li-Po type means that it wont affect so much right even he didn't use the phone it for a long time.

Empty battery within long period is bad. Your friend should keep charge it to 50%-70% if he not use it.