[Elecraft] Battery

[J. Crit Harley, MD, C.Ht.]

Traded for an used K2 (SN 556 so is an early model).
After leaving the PS charging at 13.8 to 13.9 v
(according to the K2 display)
the best the internal battery will reach is 12.5 v.
I thought I read somewhere that it should top out 
at 12.7 when fully charged.  
Question:  Is my battery "old" and unable to reach
full charge or am I mistaken about a full charge is 12.7?
Is 12.5 good enough?  Should I push the PS up a little?
Thoughts, suggestions, comments.
Tnx...Crit/K4BXN