Why won't my phone turn on?

so i had my phone for almost 2 weeks but today when I was using my phone it died so i put it on charge. it was on charge for about 2 hours and when i came back it would not turn on. so i thought it could be the outlet or something but it still wouldn't charge. but the thing when i first got it it charged pretty fast. but the day before it broke it would charged really slow. like when i went to bed it was at 5% but when i woke up it was only at 50% when usually it is at 100%.. could it be the charger or the batterie? and the batterie cannot be removed.