Only accepts certain chargers and drains battery quick

Hi,

I have a 5s that was returned by a customer. Originally he bought it and messaged me saying it was completely dead, I went to his house and tried a different wire and then he told me to change the battery anyway as it was draining fast. I changed the battery and the same thing happened again except the other wire didn't think this,

I disconnected/reconnected the battery and it turned on (with 80%+ battery) so I am thinking maybe it wasn't connected right.

Now I have the phone back and I have refunded him and I am doing more tests. The phone doesn't charge with certain chargers, I have a 5c that charges with all of them. I'm unsure of which are genuine and which aren't but I believe it won't charge to genuine ones

The battery drains fast in standby mode

Is this damage from using 3rd party chargers? What can I do to fix?