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Old 22-02-2018, 06:29   #16
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Re: Firefly's for seasonal usage

Yes all else being equal, both GEL and FLA last longer, in # cycles lifetime. GEL requires narrower tolerance on charge setpoints.

But in a some-weekends-only context and proper care, and likely stretching the 80% residual AH EoL to 70% or even 60, 8 years is possible even with Duracell AGMs at say 5-600 cycles.

Just that their FLA 6V would go much farther, all else being equal.

And so would Odyssey, just because they and Lifeline, maybe Northstar are "the best" proven AGM

does not make them better than good FLA,

especially given their much higher cost

and they do require proper care, not as robust, including that narrower tolerance on charge setpoints.
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Old 22-02-2018, 08:02   #17
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Re: Firefly's for seasonal usage

I think that Firefly’s are an excellent choice for part time boats. I just took out 8ea, 6v Lifeline’s (which were starting to bulge), and replaced with 4ea Firefly’s. With room for two more.

The one thing that you need to take in to account with Firefly’s is that they don’t like to be floated!

Both, the manufacturer and Bruce say that they are tolerant of a 13.4v float, but ideally charge and stop is the best. Hard to leave the boat for long periods with out a constant charge source, but there are work arounds.

My solution was to retain the old 12v AGM start battery and design/build a DC selector panel that when we are away from the boat, would electrically isolate the Firefly bank from the loads/charge sources and run everything to and from the start bank. This way the boat is never without a battery bank connected and the Fireflys are not on “float” for weeks or months.

True the AGM start battery’s charge profile is a bit different then the Fireflys, and I am shorting it’s life by the wrong charge profile. But the start battery is cheap compared to the Fireflys, so I have no problem with abusing it.

The dirt cheap way to accomplish the same thing is to just physically move battery cables around. But I wanted something a bit less, PITA!

Now full disclosure, I have all the tooling and equipment to not only build the needed heavy gauge cables (2/0 and 4/0 cables) but also to design and make the Selector panel. Meaning that I have a fraction of the cost invested compared to what most folks will have to spend.
You must take this into account when making the decision on which type of batteries to purchase.
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Old 22-02-2018, 08:44   #18
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Re: Firefly's for seasonal usage

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Originally Posted by Ostinato View Post
Sorry but I couldn’t agree less that Odyssey batteries work well in a deep cycle context. My experience is they don’t and it cost me a couple of grand to find out. Their TA department eventually admitted that to me as well.

Most of what you read about AGMs deep cycling is hyped in my opinion. If you want to get a more balanced perspective, read information from companies that make both AGM and gels like Victron. They more honesty represent what their batteries are intended to do.

I'd agree GCs would likely be better for real deep cycling, at least in sets of 4 or more, but there aren't as many AGM options. Lifeline, for instance. Which I've just installed (4x), to replace a bank of 3x Odysseys.

But OP's starting post doesn't make it sound like he needs too much "deep" cycling.

FWIW, that oldest Odyssey bank -- dual purpose -- lasted 12 seasons. The other Odyssey bank is about 9-10 seasons old now, I think.

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Old 22-02-2018, 09:33   #19
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Re: Firefly's for seasonal usage

if your boat will be at the dock with AC powering the charger, and you aren't concerned about weight - then I think the Fireflys are overkill. they excel at taking undercharging abuse, or having less capacity needed than other chemistry due to their ability to discharge well below 50%.

I had GREAT luck with - ready - West Marine Gels. Get them on sale. I got 9 years from my set with 425 Ahours total capacity. they load tested like almost new when I sold the boat. most of the time they could charge from shore power, but also had various cruises of 1-4 weeks with only engine alternator charging.
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Old 22-02-2018, 10:35   #20
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Re: Firefly's for seasonal usage

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I have been thinking on flooded Trojans, but they even warn against mounting them at an angle (heeling boat...). Otherwise really nice characteristics, 1000+deep cycles, but sulfuric acid is the last thing I want to see in flowing in the boat...
I have been using Trojan T-105s for a couple of decades now. All sailing conditions - including a knockdown. Never had an electrolyte spill. Maybe Trojan is nervous about liability.
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Old 22-02-2018, 11:20   #21
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Re: Firefly's for seasonal usage

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I’m surprised there haven’t been thousands of sunken boats from all the sulfuric acid (said sarcastically).
Great sarcasm.
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Old 22-02-2018, 11:42   #22
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Re: Firefly's for seasonal usage

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I have been using Trojan T-105s for a couple of decades now. All sailing conditions - including a knockdown. Never had an electrolyte spill. Maybe Trojan is nervous about liability.
Sounds good! I also suspected, that a significant spill needs time too and the boat rights itself before anything happens...
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Old 23-02-2018, 11:35   #23
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Re: Firefly's for seasonal usage

I am weekender too. I have 3x Trojan 27TMX. Was considering the Firefly too.

With 2x 50w solar, over the last 4 summers when boarding the Friday night, batteries are always full, ready for the weekend. When quitting on Sunday, batteries have been drained, about 120 to 150 amps over the weekend.
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Old 23-02-2018, 13:00   #24
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Re: Firefly's for seasonal usage

Many people size their bank so "one cycle" is 2-3 days.

As long as you can get to 100% Full (via endAmps) "most cycles" then that should be OK, but every cycle of course ideal, just unrealistic for most.

PSOC abuse IMO is when true 100% is only reached less than say 20-30% of cycles, and if that problem can't practically be solved, that's where the magic of going to Firefly (or LFP) may be worth the extra expense.
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Old 23-02-2018, 13:11   #25
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Re: Firefly's for seasonal usage

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Originally Posted by GTom View Post
how much recharge do they need after an average weekend? Are you motoring a lot/do you have a big solar or discharging them deep?
We would typically discharge the batteries 50%. We had no solar and with motor nominally just to get out of the harbor and pull the sales up and then back then which takes about five minutes each way.
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