Batteries

A couple of notes on batteries:

"Deep cycle" batteries are marketing hype. Any battery gets damaged internally every time you discharge it beyond about 50%. Regular car batteries just get damaged faster. Never discharge your batteries below 50% if you want them to last.

West Marine got with a battery manufacturer and did a lot of testing on this...

Also, to minimize run time if you are using a generator to recharge, charge the batteries up to about 85% and shut down. That's where the battery charges fastest and most efficiently, it takes a LONG time to get that last 15% to get the battery all the way back to 100% charge. If you are on solar of course, this doesn't apply because if ya got sun ya got charge. MCORPS1

So to get the most life out of your battery bank and generator (and fuel supply) you really need to size the battery bank about 3x larger in amp hours capacity than you think you will need. This lets you operate the battery bank within that 85%-50%-85% envelope and still meet your needs. It gets expensive to buy that many batteries, but in the long run it is much cheaper than burning up batteries and having to replace them more often because they are dead. Or having your battery bank wear out and go dead when the SHTF and you can't get more batteries...

Also, for those of you that live in areas where it gets cold, remember that lead acid batteries lose a large part of their amp-hour capacity when they get cold. Gel cell batteries are much better in the cold, they keep most all of their capacity. I think this also applies to AGM batteries, but I'm not sure.

If you have a way to keep your battery bank warm, that's even better. But of course warmth takes energy, and that energy has to come from somewhere, so you could end up going in circles with that one. GI8

All true, and since you mention it, 6V golf cart batteries are usually one of the best buys for a battery bank. They are rugged, have high amp-hour ratings, and are usually quite a bit cheaper (per amp hour) than the 12V deep cycle batteries. Just cable them up in a series-parallel circuit to get the 12V or 24V as needed for your system.

Which brings up another note, 24V systems are much more efficient than 12V systems. The higher voltage lets you run smaller wire sizes with less loss. Low-loss wiring for a 12V system takes big wires and lots of expense... GI8

It takes a little more shopping to find 24V equipment though, chargers, inverters, appliances like lights etc. 24V is becoming more popular in the boating world because it is so much more efficient and lots of weight can be saved on the smaller wiring.

Re: "smart chargers," absolutely. A smart charger will be labeled as such, should say something about "3 stage charger" or better, and be microprocessor controlled. A good one will also have a selector switch for lead acid, gel, or AGM battery types since they operate at different voltages. The old fashioned single-stage "dumb chargers," the kind that come in a sheet metal box, from Wal-Mart or Kragen Auto, cost $12, and buzz when you connect them to the battery... bad news. I call them "battery boilers." They will burn out a battery in no time flat.

For solar charging, the same applies. Any panel array bigger than one of the little "trickle charge" dashboard panels needs a "smart," 3-stage solar charge controller to properly charge and condition the battery bank without burning them out.

It's a cost thing.

First, you plan out how large a battery bank (in amp-hours) you need to meet your needs.

Then you go out shopping for the batteries. Since amps is amps and volts is volts, it doesn't matter what batteries you use, as long as you are comparing the same high-quality deep cycle type batteries. They just need to add up to your total amp-hour requirement.

If you shop around, you can usually find 6v golf cart batteries so much cheaper than the 12v RV/marine deep cycles that they are a better buy.

A typical example would be (and I'm making up these numbers based on experience, not referring to a bunch of catalogs here)... Say you wanted a 220 A/H battery bank. You might find 6v golf cart batteries rated at 220 A/H for $100 each. Two of them would meet your needs and cost $200.

You might also find 12v deep cycle batteries rated at 110 A/H, for $150 each. Two of those would also meet your needs, but would cost $300 total.

When pricing batteries, think in terms of "dollars per amp-hour." And make sure you are comparing batteries of equal quality, with an equivalent rating for life in charging cycles. Golf cart batteries, because of the way they are made, usually also have a very long life in charging cycles.

So when you compare all the specs and prices, golf cart batteries are usually the best deal overall in price, amp-hours, and total life.

You mention 12V golf cart batteries at EZGo, I am not familiar with the 12V version of a golf cart battery, it might be the best of both worlds, I don't know.

But for sure, I would recommend getting out of the specialist shops like a golf cart shop or a boating store, and get to a place like Costco and see what the difference in price is.

I have never really tried to compare the total weights of these different approaches, the usual rule is just that amp-hours are heavy and you can't really get around that. If weight is important though, I believe that gel cells and especially AGMs are slightly lighter than the standard wet cell lead acid, but they are also more expensive. I was just looking at West Marine and they have a new type of battery called a compact AGM, they are much lighter and smaller per amp-hour than any other deep cycle... but they are also like $624 per battery. GI8