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Joined: 25 Jul 2011
Location: Central KY
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Posts: 6128 		Direct Link To This Post Topic: Battery sugesstions
    Posted: 18 Jun 2018 at 7:14am
Originally posted by FrayAdjacent

The logic behind using 2x6V batteries is antiquated. That's a great solution for drawing huge amounts of current, like in a golf cart. And compared to flooded cells, they were more robust. 

AGM batteries are going to be as good if not better. I use a single 100Ah AGM battery. I also use a 100W solar panel with a cheap PWM charge controller. My few trips so far I have not had connections, so I used a generator, but mostly left the converter breaker off. The solar panel should maintain the battery well enough. 


actually.. no. The logic for 2 GC2's continues to be the power density and cost. While AGMs are very robust, they don't solve the density issue, and cost significantly more then a standard flooded cell.

When you start dealing with people who don't use a generator, are actually boondocking with solar, 12v batteries are very rarely used. Your 100aH AGM battery is still a lead acid battery, and not a true deep cycle, so you have around 50aH's available before damaging the battery. a pair of GC2's will cost less (often under $80 a piece) and have over 100aH's actually available with no damage to them.

Specific to the R-Pod, there isn't room on the battery tray for more then 2 12v of the Group 24 size. So, while you could get more aH's if you go with larger 12v's, say group 31's, you can't put two of them on the Pod easily. Or heck, roll big and figure out how to mount a couple 8D's.. LOL

The FUTURE is going to be LifePO4.. but as of yet, the price is still to high. The energy density, and the rate at which they can be discharged, allows them to be used as a back up to actual mains power. Some RVers have made the switch, and are reporting excellent results, even being able to run the a/c, in the desert, without a genny or shore power, but, they have +$8K tied up in the system.
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Posts: 31 		Direct Link To This Post Posted: 18 Jun 2018 at 9:42pm
Normal safe depth of discharge of AGM cells is 20% (80% discharged), not 50%. Lots of antiquated knowledge out there....

Per http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

"The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life. The negatives are slightly lower specific energy and higher manufacturing costs than the flooded, but cheaper than the gel battery."

Again, I still assert that for an RV with very low power demand, an AGM 12V battery is perfectly fine. You can find them up to 230Ah, but they get pretty heavy. 

As for Lithium cells, I watched a video where a couple in their RV replaced their AGM batteries with 200Ah of lithium cells (2x100Ah cells). Cost about $2000, but the cycle life (3000-5000 cycles) compared to the AGM batteries they were using... it worked out in favor of the lithium batteries over a 10 year period..  The number they showed was about $6000 for AGM batteries over the same period.

They did also run a large inverter off of their batteries, and could (and sometimes do) run their AC off of the battery bank. 

My 100Ah AGM battery cost about $160.. I'd have to go through 6 of them in a 10 year period to compare to the lithium. Also a lot of lithium cells like to be charged at a higher voltage than lead acid cells. I think I'll get more than a couple years out of my AGM battery just fine. I'll use my generator to power heavier loads. 
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