IPhone 4s is taking forever to charge?

Yesterday my iPhone 4s died so I put it on charge. I left it for an hour and came back to check on it only to find that it had only charged to 6%. I took it off charge as I had to leave the house and it died within 1 minute. I then had it on charge for the entire night and it wouldn't go any further than the black charging screen, as if it was waiting for it to charge to 5% then turn on, but it never did. I checked it before I went to bed and it had finally turned on but it was only at 39% (this was after having it on charge for 5-6 hours). It is now still taking so long to charge but then losing 3% battery when I use it for a couple of minutes. Does anyone know why this is happening and how I can fix it? Or will I have to take it back to the shop I purchased it from?

This could be a number of things, a short in your charger can cause this, id try using a different charger first if you haven't already. It could also be internal damage caused to the phones charging port, this can be caused by liquid getting into the port, a charger not sitting on the ports connectors properly, or even a power surge. It could also be your battery using your phone while its charging, or not letting it fully charge often enough can kill the battery even lithium ion batteries die eventually, so id try a new charger first and if that doesn't work id take it to the retailer you purchased it from for further diagnostics, good luck

As far as I know, it's not possible to "overcharge" a smartphone, despite what people say. The culprit is usually a cheap third-party charger or cheap third-party USB cable. You should always use genuine Apple power blocks and USB cables whenever possible, and try to avoid using third party chargers and chargers from different brands, especially with more expensive smartphones such as the iPhone and Galaxy S4/S5.

Third-party chargers usually don't work as well as genuine chargers do, and they tend to have less amperage, therefore they will charge slower than genuine chargers. Certain brands such as Belkin and Griffin are okay, because their build quality is close enough to genuine chargers that it wouldn't really make a difference. I'm talking about the cheap chargers and cables that cost less than 20 dollars.

You probably used to overcharge you battery which damages it or you use you phone while it's charging