Good batteries are critical, buying car batteries at Walmart just won't cut it in a PV system that you depend on for your for every electrical need. So the first rule, buy good batteries. I prefer AGM batteries, and a lot of people ask why when they are so much more expensive that lead-acid batteries, well, there are a couple of reasons. First of all the life expectancy.
The life expectancy of any battery depends on how well you take care of it. If your battery bank is to small and you routinely discharge you batteries below 50% your system won't last very long. The average Lead-acid battery will last between 3 and 5 yrs if you take care of it, keep it's charge up, keep it cool and in some cases keep adding water to it, distilled water, do you want to waste much needed space on gallons of distilled water, when you could be storing food there? The average AGM battery, 4 to 8 years, again, if you take care of it well, but in this case that means keeping it's charge up. AGM require no maintenance, meaning no adding water and no storing distilled water. AGM batteries are sealed so you couldn't add water if you wanted to, which brings me to the next reason why I favor them so.
Lead-acid batteries put off fumes that, in the right circumstances can be explosive, yep I said explosive. Do you really want to have to worry about that? AGM batteries as I mentioned earlier are sealed, so, they put off no fumes. However, they are susceptible to expansion over time so don't put them in a tight fitting box. They have been known to split in extreme cases so as with lead acid batteries don't put your battery bank inside your home unless you have no other choice and if you do, be sure to have adequate ventilation.
In my previous life(life before prepping) I lived aboard a 36ft sailboat, not always in a marina, sometimes I lived on the hook(at anchor). As you may or may not know, sailboats heel(tip to one side of the other) when under sail, and they are constantly in motion if not on land, a sealed battery won't leak in those situations, they won't leak in any situation for that matter , even if stored on their side, so they were the right choice and a choice I made before I really knew what the hell I was doing, thankfully it was a good one. Another advantage to AGM batteries, they aren't susceptible to freezing on the boat that wasn't a problem they were below the waterline so they stayed at roughly the same temp as the water but in an off grid situation this is a real plus as I am pretty sure they you won't be keeping them in a heated space, well, that is if you follow my advice about not putting them inside you house.
Charging voltages for most AGM batteries are the same as for a standard type battery so there is no need for special charging adjustments or problems with incompatible chargers or charge controllers. Because of their design integrity, AGM batteries can be recharged up to 5 times faster than a regular wet cell battery. In a PV system that is a god send, especially if your not accustomed to being extremely energy conscious. Another huge plus if this is your bug out spot instead of your full time home, an AGM battery when left unattended will only discharge at a rate of up to 3% per month and even after 12 months sitting idle can be recharged and put back into full service with no ill side effects. A normal wet cell battery discharges at a rate of up to 4% per week.Yep, I said 4% per week!
Well that is the end, I will be covering more on batteries in future articles...