Lupine 6.8Ah battery re-activated

I have an older 6.8 Ah battery that is acting strange. First, it seemed totally dead and would not light up the lamphead at all so I applied the trick of "activating the dead battery" by using the 12V adapter and attaching it to the positive lead for about a minute. After this, I left it on the charger overnight but I never got a green "fully charged" indication. However, when I plug the battery into the lamphead, I get 8 blinks of the blue LEDs indicating 8 volts.

I decided to do a runtime test on this battery after leaving it on the charger overnight. The green light on the charger never came on to indicate the battery was fully charged.

Lamphead: Wilma 15W
Setting: 12W power setting, run at 100%
Calculated Runtime: 6.8Ah * 7.2V/12W = 4.08 hours
Actual runtime: 4 hours, 36 minutes
Location: 62 degrees, basement with fan running 4' away

So it appears that my battery is fine but why doesn't the green light on the micro charger come on like it does with my other batteries? Any else seen this before?