Battery percentage going down but its charging

"You said you have to jiggle the charger to get it to work?

If you have to wiggle/jiggle or biggle (my new word:) the charger in the port to get it to charge it's most likely losing connection to the traces on your motherboard. We've seen this a lot on the S3 in my store. If the charging port inside looks normal (no bent pins or damage) its possibly damage to the traces on the motherboard that connects the charging port to the motherboard. Unfortunately when this is the case I recommend another device or motherboard. You would basically need super human eyes to fix this part of the board. Even if you replace the charging port it might be a temporary fix if the connection to motherboard is poor/damaged.

I'd first inspect the inside the the charging port (see if there's any visible damage). I would say try a battery or another cable but if you have to adjust the cable, it prob won't work. I'll upload a picture of what I'm talking about soon."

faulty battery , If phone is as old as stated you should have manufacture warranty

"I'm an electrical engineer... The problem, more than likely is the c-type connector head (the end piece that plugs into your android phone). The trace pins are precision soldered with a wave machine to the specific pin contained in a wired harness. If you happen to drop the phone in any way on any surface at any distance, it's quite possible to damage that precise harness inside the connector head causing the power dissipation of the battery due to the current now being unconditioned. This is a safety feature so as to not explode the phone's battery when those trace elements are damaged. (it's like the surge protector in the cable is broken) I'd recommend getting a brand new undamaged cable and reboot the phone before charging, this in all likelihood will fix your issue but I'd definitely stop using that cable. You'll eventually burn out the elements in the adaptor (the pronged piece you plug into the wall outlet) too causing it to be bad and then you'll end up damaging any new cable you plug into it. GO WITH A HEAVY GUAGE BRAIDED CABLE WITH HEAVY DUTY GROMMET CONNECTOR ENDS ON BOTH THE USB AND THE C-TYPE HEADS. (you can get fairly good ones on Amazon)

SIDE NOTE: charging cables were designed to be used when the phone battery is fully discharged and would require the phone to be in a stationary horizontal position with zero cable bend even when using it with a laptop as a data transfer cable as well. (this means learn to stop talking or operating the device while charging for best results... the cables will last much longer that way)"