Firefly AGM and A Larger Electrical Project?

[FlyMeAway]

After a cruise gone somewhat awry, it's become clear that our house and engine batteries need replacement (and probably the thruster batteries while we're at it). I've done a lot of battery research and am pretty keen on the Goldilocks of Firefly Oasis Carbon Foam AGM for our house batteries (regular AGM too many issues, lithium too expensive, Firefly just right!), while sticking with either Concorde or Northstar for starter/thruster batteries.

I have a bunch of questions as I undertake this project and would love some input from other owners.

Related to the Firefly AGM specifically:

• I've done some searches and looks like a lot of people have considered Firefly, and maybe a few have installed. Would love some reviews/thoughts after living with them for a few years
• For those who installed them: did you just drop them in? Did you mix and match with different thruster/engine batteries too? Most importantly, did you get some kind of charge controller for them (I understand they can charge faster than a lot of AGM but that requires more hardware)
• Is the general consensus to use starter batteries for the thrusters?

And then questions about some additional electrical projects:

• What advantages might I get from replacing the solar controller at the same time? Would probably go Victron. I've seen a lot of people talk about this upgrade but I don't understand the advantage over the OE one
• How about an alternator upgrade? Is this worth it as well?
• For battery monitoring systems, any suggestions?
• Ok, if I go Victron for solar and monitoring, should I just throw in the towel and swap out the inverter while I'm at it? 😀

Our boat has three co-owners with different styles of cruising, but two of us really like to spend time a few days at a time on the hook. The battery upgrade is aimed at that use case and we'd like to significantly mitigate electrical anxiety when cruising.

 

[Submariner]

Related to the Firefly AGM specifically:

• I've done some searches and looks like a lot of people have considered Firefly, and maybe a few have installed. Would love some reviews/thoughts after living with them for a few years
• For those who installed them: did you just drop them in? Did you mix and match with different thruster/engine batteries too? Most importantly, did you get some kind of charge controller for them (I understand they can charge faster than a lot of AGM but that requires more hardware)
• Is the general consensus to use starter batteries for the thrusters?

And then questions about some additional electrical projects:

• What advantages might I get from replacing the solar controller at the same time? Would probably go Victron. I've seen a lot of people talk about this upgrade but I don't understand the advantage over the OE one
• How about an alternator upgrade? Is this worth it as well?
• For battery monitoring systems, any suggestions?
• Ok, if I go Victron for solar and monitoring, should I just throw in the towel and swap out the inverter while I'm at it? 😀

I have 3 Firefly G31's installed. They were drop-in replacements for the factory OEM batteries.
I do not recommend mixing and matching them with the thruster or engine battery. The engine battery should be a starter battery, not deep cycle. The thruster could be a deep cycle or starter. But since Firefly batteries have a much deeper discharge than conventional AGM batteries, if you were to tie in your thruster battery with a house battery bank of Firefly's, it's likely you'll damage the thruster battery via excessive discharge.

Firefly batteries don't require anything specific in comparison to AGM. They use a normal AGM charging profile. But to fully re-energize them after deep discharges, firefly's require a minimum of 20% charge rate (approx 25 amps per G31 battery). I kept the factory 20 amp battery charger and I added a 70 amp charger. 90amps combined gets me to 25% charge rate.

The thruster could be a starter or deep cycle, as even the factory OEM deep cycle batteries have about 530 CCA's. Firefly G31's offer 600CCA.

For battery monitor, I'd recommend a Victron BMV 712 Smart battery monitor.

For solar, I have 2x200 watt panels (400 watts total).
I would recommend upgrading your solar controller from the PWM style to an MPPT controller. I went with a Victron MPPT Smart Solar controller, 100/30. The instrumentation alone is worthwhile. Plus the MPPT controller is about 20% more efficient on the larger panels (i.e. more sunlight converted to amps).

With the Yamaha F300, the alternator is a 70amps which I've seen it put out upwards of 45 amps at cruising speeds. It outputs about 20 amps at idle.

The inverter is up you what you do with it, ours is the factory OEM Kisae 2000 watt pure sine wave. It works well and I have no plans to replace it.

 

[FlyMeAway]

I have 3 Firefly G31's installed. They were drop-in replacements for the factory OEM batteries.
I do not recommend mixing and matching them with the thruster or engine battery. The engine battery should be a starter battery, not deep cycle. The thruster could be a deep cycle or starter. But since Firefly batteries have a much deeper discharge than conventional AGM batteries, if you were to tie in your thruster battery with a house battery bank of Firefly's, it's likely you'll damage the thruster battery via excessive discharge.

I'm confused about this and your other comments below. You say you don't recommend mixing, but then you say that the starter and engine batteries should be different. Did you end up using the Fireflys for house, starter, thruster, or a different battery type for starter/thruster? How did you resolve the excessive discharge issue?

Firefly batteries don't require anything specific in comparison to AGM. They use a normal AGM charging profile. But to fully re-energize them after deep discharges, firefly's require a minimum of 20% charge rate (approx 25 amps per G31 battery). I kept the factory 20 amp battery charger and I added a 70 amp charger. 90amps combined gets me to 25% charge rate.

How was the additional charger wired? Which 70 amp charger did you use? And what is the total AC current draw on the 70 amp DC charger? Getting to 25% charge rate for 4 house batteries (25 amps each) could be challenging...


Thanks so much!

 

[Submariner]

My thruster battery is factory OEM, Universal deep cycle.AGM
My house battery bank consists of 3 G31 Firefly batteries. AGM
My engine battery is factory OEM, Starter battery, AGM

Being that all 3 banks are AGM, they all use the same charging profile (which I've fine tuned for the voltage specific to the Firefly's since they get the most cycling).

All three banks are separate. I do not ever parallel my thruster with my house bank as they are dissimilar batteries in that the firefly's can deep discharge much lower than the factory OEM battery can. My thruster battery is exclusively for the thruster.

The engine, house, and thruster are connected via the ACR's, which allows for engine charging and solar charging to hit all three battery banks. This also allows the battery charger(s) to hit all 3 banks. The ABSO Factory charger has 3 outputs, one for each battery bank. The 70 amp battery charger is just wired to the house battery. It will charge the engine and thruster battery via the ACR's.

For battery charging, I added a Victron Skylla 70 amp battery charger to the boat. I wired it into the AC panel on an accessory 15 amp (120volt) breaker. It'll pull at most, 10.5 amps from shore power. I run it in parallel with the Abso 20amp charger the boat came with and get 90 amps at 12 volts going in. If I'm out cruising in the middle of the day with the solar (400 watts) going and the engine running, I've seen as high as 60'ish amps going into the house bank. (40+amps from the engine, another 20+ amps from solar). Still short of the 20% minimum. But it's the best I can do.

When comparing the Firefly batteries (75Ah usable out of 116ah) to the Factory OEM (50Ah usable out of 110ah), three Firefly batteries are the equivalent of 4.5 factory OEM batteries, based on usable amp-hours available. More wattage less space and weight.

If you don't hit the minimum 20% recommended, expect the Firefly batteries to lose capacity over time. The capacity is recoverable only via enough amps fast enough to re-energize them back to 100%. How much capacity is lost over time, I've no idea. But it's not lost forever if you can zap the batteries with enough current. The Factory OEM batteries support a max.3C charge rate (30% of 110ah = 33amps / battery). The Firefly's support a max .5C charge rate (50% of 116ah = 58 amps). A huge advantage of Firefly's are their ability to absorb charge much faster than conventional AGM. This would be most beneficial for someone who runs a generator on their boat. The 20amp battery charger that came with my boat is about 240 watts. To run a 2000 watt generator and consume only 240 watts seems unreasonable to me. To put in 90 amps (about 1100 watts) not only takes less time, charges the batteries with what they need, and would utilize the generator the least while providing more economical output.

With the 3 Firefly's able to accept a total of 174 amps, I can't come close to generating that much. But I am able to at least hit the 20% minimum with my two battery chargers. If I were at a guest marina and my battery bank was really low, like down -250ah... I'd plug into shore power for +90amps, solar would give me another +20amps, and I'd idle the Yamaha F300 for another +20amps, total: 130amps of charging. I'd be back to about 85% SOC within 90 minutes.

Here's a video we published regarding the installation of the Victron Skylla 70 amp battery charger.
https://youtu.be/CH85BebaGy4

Upgrade to two Firefly batteries.
https://youtu.be/AehPUYetDzU

When we added the third Firefly battery
https://youtu.be/HJu3UsbGMq8

Upgrading to a Victron MPPT 100/30 solar controller
https://youtu.be/2NAqsXN8BDk

Upgrading solar power to 400 watts
https://youtu.be/M_BzO5R1AD8