Dead Lipo??
 

I got a used Venom 5000mah 2S removed from the hard plastic case free that came with a FT TC3.

However whenever I charge it...it will never reach its peak even after 10-12 hours. I have to give it a quick boost charge in NiMH mode first in order for me to balance and charge at the same time (I use a Hyperion EOS0606i)

The cells are not puffy or punctured. I'm thinking the previous owner probably ran the pack without LVC on. Am I right to assume this?

It will not hold any voltage if left sitting more than a few days.

It could be old and used up or could be badly damaged, hard to tell. Could have been left in his RC with the esc still connected and drained that way.

Regardless, its done, even with you jump starting it, it prob doesn't have the punch it should.

+1 It definitely sounds like it is just an old battery to me. Maybe it was run past cut-off a couple times maybe not, but it definitely sounds that the poor battery has seen its time..