Recently we had two battery choices in RVs. One was to use a lead acid battery, usually AGM and the other was to use a lithium battery, usually LiFePO4.
I've added a link to a 2015 article about these "Carbon Foam Technology" batteries at the end of this post and a link to the manufacturer's brochure. Please note that I am not endorsing this product as I do not currently own it. But it seems to be the poor man's lithium battery and I will definitely consider upgrading to it when I next change the AGMs.
Comparing benefits and trade-offs to each (AGM versus Lithium):
- AGM batteries are relatively inexpensive, but can only provide about 700 charge-discharge cycles if operated to 80% DoD (depth of discharge). That's perhaps four years if there is a charge-discharge cycle every other day. The cost for 220Ah batteries is about $450.
- Lithium batteries are relatively expensive, but can provide 2,000 cycles under similar conditions at a cost of about $1,939.
Carbon Foam AGM Batteries
There is a different design of AGM battery available that promises longer life at 50% and 80% DoD. This battery has been in use for about 8 years. The Carbon Foam AGM battery is more costly than a standard AGM, but significantly less costly than a Lithium battery. Yet, it has similar performance characteristics to the LiFePO4.
Advantages and disadvantages of the Carbon Foam battery are:
- Can be repeatedly used to 80% DoD. "Depths of Discharge to 80%-100% of rated capacity without any loss of performance."
- Can provide 1,000 deep discharge cycles 80% DoD. That's about 1.4 times normal AGM batteries.
- Can provide 3,600 cycles at 50% DoD. That's 3 times normal AGM batteries. (Manufacturer states life is 3,600-4,200 cycles at 50% DoD).
- Can be stored in a partially discharged state.
- Faster recharge (see end of this post).
- Cost is about double that of normal AGMs. (My 220Ah cost about $490 installed). The AGM batteries currently in my coach are stated to provide 700 cycles at 80% DoD. The cost advantage of the carbon foam battery diminishes as the DoD increases.
- Like AGMs, can be recharged at temperatures as low as (-)4F (operating range is -4F to +131F).
Technology
According to the manufacturer, here is what is different about the Firefly Oasis AGM battery: "The Oasis uses a patented microcellular carbon foam grid imbedded [sic] onto the internal negative plates. This grid prevents large sulfate crystals from forming, thus the sulfate will easily dissolve back into the electrolyte with a full charge. For a full capacity recovery, no “equalization” is required with Oasis. Only do a full recharge as needed to “open up” the full capacity once again. There is no permanent damage or capacity loss from extended PSOC (partial state of charge) operation, or from deep discharging to a low SOC (state of charge)."
Link to 2015 Article:
https://www.practical-sailor.com/blog/Can-Carbon-Foam-Batteries-Meet-Hype-11694-1.html
Recharging
"The Firefly showed to have charged at a faster rate than a smaller capacity AGM battery. That, coupled with the fact that there is no need for it to be fully recharged each cycle, makes the Firefly Oasis Gp31 the closest thing to Lithium in charging performance, and has established itself as the gold standard of Lead Acid AGM batteries."
Link to the recharging comparison article:
https://coastalclimatecontrol.com/index.php/blog/186-firefly-batteries-new-testing-reveals.html
Manufacturer's Brochure
Link to a pdf of the brochure:
http://fireflyenergy.com/wp-content/uploads/2017/08/12VG31-brochure-SPI-LV-1.pdf
