IPhone 4S battery slow charging

My wife's iPhone only charges to 51% overnight.

Does it need a new battery or is it sign of something more serious?

Hi, do you close all programs down, before starting charging?

Advice: double click on home button, all open programs in scroll, swipe up to lose each one

Then charge, using an apple charger, not clone.

Hope this helps you

It is rather old now and rechargeable batteries only last a certain amount of time.

It could also be the indicator isn't quite right. I had a look for my girlfriend and it seems to solution can be; charge it fully, use it until it dies, fully recharge it again, use it until it dies again then recharge. It should reset what it thinks empty/full are.

But as said, it would be worth looking for a new battery as I'm guessing it's over 3 years old now?