My battery cannot sustain its charge!?

ive got an iphone 5, ios 9.2.1, 12 gig capacity.

my phone will simply not charge.

even after being on charge for hours, i use it for a fe mins and it drops

i tried switching the lightning cable, i used a differnt means of switching.

i let the battery drain before attempting to fully charge it, but after being on charge the whole day, it got upto 56% and on removing it from charge, it dropped to 12 in 5 minutes.

ive tried forcing a restart.

Idk what it could be. PLEASE HELP!! dont want to have to buy a new phone 😐