I worked on a friend's Iphone 5c that had an issue that would cause the battery to only last about 20 minutes, despite being fully charged. This would lead to several issues, such as the screen dimming and not working properly. Of course the battery needed to be replaced. Unfortunately the Iphone 5c does not have a removable back cover, so replacing the battery is a bit more difficult when compared to other phones.

FYI, I should mention that I purchased this battery from Amazon.com. Altogether it took me about 30 minutes to get the battery replaced. It's not as difficult as replacing other Iphone 5c parts, but it can be a bit tricky. You will need a pentalobe tool to remove a few small screws from the phone. I would suggest getting one if you don't already have it.

These are the two pentalobe screws that I referred to before. You'll have to remove these screws to get access to the inside of the phone. These weren't difficult to remove, but they can strip if you apply too much pressure.

Next, you'll have to remove the screen. I used a spudger to get under the screen, but this does not come with the replacement battery. However, if you don't have this you can probably use a credit card, or anything that's small enough to get under the screen and lift it up. There are clamps around the entire screen and these will disconnect after slightly lifting the screen. These clamps on the screen are a bit tough, so you will have to put in some work here.

This photo was once I finally got the screen off. There is a metal piece on top of the battery cable and this has to be removed to disconnect this cable. I circled both screws that I had to remove from this cover. These screws weren't difficult at all, so they should just come right off. Once you get these two screws off, the metal piece will just come out of place.

This photo was after I got the metal piece removed. In this photo I circled the battery cable which is on the main board. I just inserted the spudger under the front end of this cable, and it popped up without any difficulty.

This was once I got the battery cable disconnected from the main board. When putting this cable back on you don't want to cause any damage, so just be sure to match the grooves on the cable with the grooves on the main board to avoid any damages.

The most difficult part for me was when removing the battery from the frame. Apparently there is adhesive underneath the battery, which holds it in place, and this stuff is extremely tough. I initially wanted to insert the spudger under the side to remove it, but there was no chance of removal. I eventually ended up using a heat gun on the backside of the phone to melt the adhesive. Melting the adhesive won't necessarily remove all difficulty because you will have to continue to pry under the battery to get it off. However, I eventually got it off after about 10 minutes.
This is the new battery as it put it in place, and put everything back in place. I did not have to put any adhesive on the backside of the new battery because there was plenty left on the frame of the phone, so I just stuck it in place. Everything else went on exactly as it came off, and I don't want to be repetitive by going through it precisely. However, the pictures are exact so you should refer to them if you have problems putting something back on.

Once the new battery was installed, it worked exceptionally! The old battery only lasted about 20 minutes, but the new one lasts about 9 hours, which is a significant difference. There were some tough parts in removing the old battery, but I have no complaints once it's installed. I would definitely recommend it!