How long to idle to charge battery?

First off, nobody here is wrong except for anyone who would fully charge a very low battery with his charging system. HF has their version of the battery tenders on sale frequently for around 6 bucks each. I keep one on my emergency generator at home. When I attended a Honda school many years ago, it was explained that when you charge up a very low battery from your charging system you are potentially ruining a perfectly good battery....slow charging's best. I realize this choice is not always an option. Normally riding down the road, your regulator keeps your battery charged in little spurts as needed. If your battery's seriously down, the regulator dumps all the amperage available from your charging system into that battery. If this happens to be for an extended period of time, the battery can get hot and the plates inside warp and touch each other.....POSSIBLY(not always) ruining or otherwise decreasing the full functionality of the battery. A low amperage slow charge won't threaten the battery's longevity with the high heat. My suggestion would be (if not using a tender) and you really just HAVE to do something is to check your battery's voltage with a multitester. If you're around 12.5 or more Volts, then I wouldn't worry about it