Probably a smart idea would be when our batts are getting low would be to hookup a headlight or two and let them go flat before recharging. That's what I do to revive them. I have an old fashioned charger with a manual setting. I sometimes charge 'em back up way over 13V, then, of course, discharge them all the way again. I'll also trickle them for a week, then discharge. An epsom salts solution is employed for most of this. Once I like where the battery is, I strain and replace the original electrolyte, which oddly is gray, not clear, but works just fine. Some like to replace with fresh electrolyte, which I'm sure wouldn't hurt.