the blur

I normally hook up my battery tender without doing anything special.
this time the light sequence on the battery tender was showing 80% charged, no problem so I thought, but the battery was still dead.
car would not even crank.

so I disconnect the battery from the car, and then hooked up the battery tender. now it shows the true condition of the battery.

some how with the battery being connected to the car, the battery tender wouldn't properly charge the battery.....

engle1147

How old is the battery......still good?