S4 battery drain whilst charging

[Spring Roll]

Hi, I've had my S4 for almost a year now. I unfortunately, after a few months, started to notice the battery wouldn't last a whole day of minimum use, with power saving mode on etc. I haven't really gotten round to getting a new battery for it yet. However, today, I was plugged in charging my phone (with an iPod charger + the mini usb which came with the s4 as the original charger made a horrible noise when it was in use) I was playing a game (which is what I usually do whilst it's on charge; however the battery life was draining and it eventually died. When I turned it back on it said it was on 0% and charging but it wasn't actually charging and everytime I tried to do something it turned off. I turned it off and left it plugged in for about 2 hours. When I returned it was around 47%. I turned it on and started to use messenger and instagram. However the battery started draining again; which has never happened when I've been using it plugged in.
Will a new battery or charger fix this? Or is it the usb socket on the phone?
Thanks for your time and hopefully you can understand my issue through my muddled tale.

 

[SpookDroid]

I would try a different charger first, if you can get your hands on one. If I recall correctly, iPod chargers are 0.5Amps, iPhone ones are 1A, but the original S4 charger is 2A. So the higher the Amp output rating, the faster your phone should charge, provided everything else is fine with the battery and charging circuits. Also check your Battery Report in your phone to see if any unusual apps are eating up the battery.