[Brian in Tucson]

If you're going to go big and replace the battery, AGM sealed batteries are available in auto sizes and configurations, and some are not vented so they don't outgas. The way I would do it is to charge the battery with a regular charger and then using any of the methods mentioned, keep it on a battery tender for the off season. Battery tenders are very low amperage, so charging is slow--and hydrogen molecules are the smallest in nature, so they will leak out through zippers or even plastic. I look for them at garage sales, both my Battery Tenders (TM) were less than $10.

My battery isn't a generic, the PO bought a Bosch as a replacement. To tell the truth, it's just a battery, paying more for it is just paying for a label. Walmart MAXX batteries have served me well and you can afford larger capacity--which will (imho) last longer. BTW, I have a little digital voltage gauge mounted in the left side cigarette lighter spot. Turn on the key to check the battery voltage.