Charging symbol is there but won't increase and sometimes decreases

Hi, sounds very likely just a bad battery. First swap the battery to rule that out....make sure it's original if possible. Then swap the charging port to rule that out. If those both fail it's most likely your tristar chip on the board. Are you using original or aftermarket chargers?

Hi. Sounds annoying that it won't charge.

Well, first of all, be sure to check that the chargingcable isn't the problem. Buy an original Apple Lightning cable.

Double check, that it isn't the lightning connector, that is broken. It's quite hard to say, so if you where me, i'll fix it myself and get a new one. It's cheap, and nearly easy to fix. I'll give it a shot. Lokk here for a Lightning connector replacement.

Still, if that didn't work, try replacing the battery. But, it sounds like it isn't the battery, that isn't the problem. Lokk here for a battery replacement.

Well, because it's over 1 year old, the warrenty isn't there anymore.

Wish you the best luck, cheers.