[Lee]

After some obs maintenance yesterday I left the lights on, so found my two 9Ah 12V SLAs running at 8.5V or so....
One of them seems to be trickle charging off the solar, the other seems to be getting nowhere, ie still reading 8.5V. I've put it on a 'Battery Fighter' charger, and the voltage seems to jump to 10.5, then back to 9V every 30-60s or so. Is it dead? Can it be revived?
I'm going to make some timer switches I think to avoid this, I replaced one last year after the same thing happened - so before I buy some more batteries, any tips to rescue this one??