1. The phone cannot be turned on if it is not used for a long time
Charge or replace the battery for a long time.
This is because the battery voltage is too low if it has not been used for a long time. You can try charging it first. Do not abandon. because there is no response when plugging in the charger or it cannot be turned on. Charge it for a while. Check if the voltage can return to normal.
If it still cannot be turned on after charging for about 1 hour, it means the battery has been permanently damaged. In this case, the only way to replace the battery is to replace it. to find a way. You can buy a new battery online and figure out how to take it apart and replace it yourself, or you can go to a repair shop to find someone to replace it.
The lithium battery of the mobile phone will have a certain degree of self-discharge even if it is turned off. Over time, the voltage will drop to a very low level, and this will overdischarge. Damage to lithium batteries is relatively extensive and can cause irreversible damage. Therefore, if the mobile phone is not used for a long time but wants to be used again in the future, it is best to leave it fully charged and recharge it every 2 or 3 months, for example.