Is this a sign of a dying battery?

[tolum]

Guys, need your advise on that. This morning my car wont start. Battery was 10 vdc. I jump it with my other car, Boxster starts. Took reading on battery when running, I get 13.75 VDC steady with engine running idle. Stop car, reading goes down to 11.89 vdc and slowly going down by 0.1 volts every 5 minutes... Is this a sign of s dying battery?

Thanks for your help.

Thierry