I'm using a Deltran Battery Tender Plus
Battery Tender® Plus
That's a link to the exact unit I'm using... I'm now beginning to question it though. How long should it take hooked up to that thing to charge my dead Boxster battery? I've done two 12 hour charges on the battery, but it still isn't registering as fully or even 80% charged. I read the manual from the charger, and if the battery is below 3 volts, the unit will flash red and not function (built in sensor from what I've read). However, whenever I hook this battery up to the charger the steady red "charging" light is on leading me to believe all is functioning properly.
To see if the battery was bad, I took it in to Advance Auto parts and had them test the battery on their battery tester. Elmer, the battery guy, was surprised that the battery in fact tested good! Here are the results from the battery test:
Results
Good- Recharge
Voltage: 12.30V
Measured: 820 CCA
Rated: 690 CCA
Temperature: 74 degrees
"Battery meets or exceeds industry specifications, but is low on charge."
Should I just continue charging with the old Deltran is do you guys think something else is going on here? I'm interested in your thoughts... Thanks again!