I'm trying to start my 340 Duster a fairly major engine combo change and EFI conversion. After several failed attempts I've started looking at things outside of the EFI settings. The car has a Optima red top that I noticed was dated 11/11 (time flies when on jack stands). The car sat dormant for several years and I rarely put a battery tender on it, but voltage always seemed to be 12+ when I checked. I have been using a tender as I've started to wrap up the EFI install.

Yesterday I had the battery load tested at Advance Auto. At 76°F and 12.3-12.4V the battery showed 635CA when it is rated for 800CA. I trickle charged it back up last night and 12 hours after removing the charger it is back around 12.3V. Is this a sign of a weakened, but not dead battery? I plan to pull one out of my cummins to try starting the Duster with tomorrow.