Battery Not Charging?

[regnaleb]

Hi guys i need some help.. Theres a few problems a need to fix before i get my car on the road and this is one of them. Hopefully someone could help me out and it will be appreciated immensely. I own an s13 with a type x sr20det swap. Everythings clean and i have a WS harness for lower and upper.

here goes, first i would like to start off with my mistake. I hooked up the battery connections backwards and fried my atl fuse along with my harness and ignitor chip.

lol with that said, i replaced everything and the car now runs. ONLY when i boost it with another car.

So i boost it and it runs, i disconnect the jumper cables and the car runs perfectly for a long time, had it running for a good twenty mins before i turned it off. I didnt let it die

When it was running i read the voltage meter on the battery and it was reading 14 volts but when i turn the car off, the voltage slowly drops on the battery. maybe like 2 volts a minute... Im wondering why its not holding its charge? Is this a sign it could be a dead battery? like completely dead beyond revival?

maybe someone can clarify some things for me and lead me in the right direction to getting this fixed. Thanks guys and girls