When looking at Firefly batteries don't forget to include the fact that they are
designed and
intended for PSOC use to 80% DOD, then cycled back to 80-85% so you are actually using 60-65% of the battery, even when out cruising, vs. just 30-35% with other flooded or AGM batteries.
Also that 80% DOD often chops an entire AGM out of the equation so the $486.00 per battery becomes a much more equivalent deal when you need only three vs. four of the competitors.
The cost of lead acid batteries, not just AGM, can not be judged on the box price alone. Ah capacity, projected cycle life, usable capacity, and lifetime watt hours or Ah's delivered are what will determine actual battery cost over the long haul. Many of my sailboat customers can murder batteries in less than 100 cycles regardless of flooded or AGM and this is due to PSOC use & sulfation.. Many of my trawler customers can murder them in less than 150 cycles for the same reasons. Was on a GB-32 yesterday and the flooded deep cycle Trojan's were sitting at 12.32V when I got on-board. They are three years old and ready for the recycle bin. Why? PSOC abuse.
The box price for Firely is now certainly higher than other
premium G-31 AGM's (Lifeline, Odyssey, Northstar) but
box price alone does not equate to value.
If you want to consider East Penn a
premium AGM please read the May 2015 issue of Practical Sailor and see how they dealt with PSOC abuse.
When you consider that the other batteries should only be cycled to 50% DOD, in order to maximize cycle life, and they don't handle PSOC use nearly as well, it certainly makes a strong case for these batteries not costing as much as they may
appear to, when judged only on the per unit price.
For example: (current street price from my distributors)
Three Firefly G-31's = 330Ah - At 80% DOD =
264 Usable Ah's - $486.00 X 3 =
$1458.00
Four Lifeline G-31's = 420Ah - At 50% DOD = 210 Usable Ah's - $370.00 X 4 = $1480.00
Four Odyssey G-31's - 400Ah - At 50% DOD = 200 Usable Ah's - $377.00 X 4 = $1508.00
Four Northstar G-31's - 404Ah - At 50% DOD = 202 Usable Ah's - $390.00 X 4 = $1560.00
Also with the Firefly battery at 80% DOD this means you are in the very efficient bulk charge stage (constant current) far longer than if we started at 50% DOD. This means considerably more
usable energy can be returned to the bank in a shorter time frame than with an AGM that is only cycled to 50%.
I have a fair number of Firefly banks out there, I even run one on my own boat as a reserve bank, (LiFePO4 primary) and a lot more scheduled to be installed and I can see the value in them for certain types of cruisers...
I still install a lot of Lifeline, Odyssey, Northstar, Trojan, Crown & US Battery etc. too.
I buy my Firefly batteries From Bruce at Ocean Planet Energy but he has a number of distributors throughout the US. If you are in the Chess Coastal Climate Control is also a Firefly dealer.
When Bruce first mentioned the Firefly battery to me I basically called BS on it. I then designed a test protocol to simulate typical marine use that I witness on cruising sailboats to see if it was actually any different than the other AGM's. Unfortunately my
assumptions about the Firefly were misguided and wound up eating crow on my BS call...
Partial State of Charge Test May 2015
Partial State of Charge Test August 2015
I believe myself and Nigel have the oldest Firefly's in the marine market and both of these banks have had the living snot beaten out of them. Both Nigel's bank and my own Firefly's still capacity test at 100% of initial tested Ah capacity.
I no of know other battery, flooded or AGM I can say that about. Even GEL batteries don't stand up to the cycling abuse I have thrown at the Firefly's, and GEL's are excellent deep cycling batteries despite needing very careful charging.
Despite only being a few years into Firefly, in the marine market, they definitely do separate themselves from the pack when dealing with a PSOC environment.
For trawlers the reduced weight of additional batteries and PSOC are a bit less of an issue than they are for sailboats, but still can be important for those who cruise regularly.