Why does my Samsung Galaxy Core Prime's battery go down so quickly?

[AC Question]

I was on my phone as i normally do and it went down to 15% so it showed the 'Battery is low, please connect charger' sign for a fraction of a setting before it turned off almost immediately and when i put it on charge and turned it back on it was on 0%. My phone has been going funny lately with my signal going weird (having full bars but cant send a text) and my battery has been going down awfully fast. Also my chargers have been going funny and sometimes when i put my phone on charge the charging sign doesnt show up but when i restart my phone it shows up again. I just mainly need help if there are any ways i could possibly fix it or if i need a new battery because i have heard of this problem and i feel like i might need to buy a new battery, anyway i would love to have some help.