LifeP04 oasis fireflys battery to battery chargers

[Eastward ho 24]

It’s time to redo my whole entire electrical from the ground up.alt,reg,belt kit,and battery bank. I was going to go with firefly (3) 4v agm @ 450ah, but Battleborn (300ah)lifep04s aren’t much more. I can get 275ah useable from 3 Battleborn for less then 3k compared to 225useable (3 4v in series) for 2k Looks like the fireflys are close to the lifep04 in life cycles ( fireflys 4v at 4900 @60% dod vs 5000 @ 90% dod) As far as useable ah, the lithium get the edge. But who really cares about useable ah if I need 200ah useable, and I have to buy 400ah to get it and the 400ah is less money so be it, and I don’t really care about weight its a cruising boat. So the only edge of the lithium is constant voltage and recharge time in my eyes. I feel like the rest is all marketing fluff. I can’t find much independent info and real world reviews on the fireflys (I’m talking. About the 4v fireflys). But it does seem that the 4v firefly seems to be a REALLY REALLY REALLY good battery almost as good as the lifeP04.if you write off the weight savings, and useable ah ( because you can just oversize the firefly bank)as advantages. That leaves me with. The fireflys are cheaper ,have 4900 life cycles at 60% dod. They don’t require special charge parameters and don’t leave your alternator running wide open all the time. The lithium’s only edge being they charge faster can pull a larger load at once( I don’t have any large loads that I wouldn’t run unless my motors running)and remain at constant voltage. But this is at the expense of more pieces of equipment, more money, more wires,more components,more things to go wrong,and more stresses on alternator. Am I missing something here? So for me the only advantage is faster recharge time..how much faster does any one know? I have yet to add solar and or wind and the faster recharge times will help here but is it enough to justify?

I have a yanmar 3gm30f I’m going to add an electromaax 160amp alternator and emaax external regulator with their belt kit. 3 100ah Battleborn. They have internal bms and I don’t want to fry my alternator once the lithium’s are fully charged and the bms disconnects. From what I read I can use the sterling battery to battery charger, then I’d be charging my lead acid start battery from the alternator and mynlithiums from this. But I was thinking is this going to restrict my charging times? Is there a situation where ; my alternator is set on lead and it floating and my lithium’s are say 40%dod will my lithium’s be in essence be on float? Am i negating the lithium’s faster recharge times by using a battery to battery charger? Or is there a better way to protect my alternator from bms?

I don’t know if the marketing hype from the manufacturers or lithium’s gotten me. Or if these 4v fireflys are a better route.

[yalla]

Great questions!

(<-- that means I look forward to hearing more... i.e. opposite of being bored)

[flyboy62000]

I just did this on my boat and had the same questions. I went from 2 x 110AH (130 usable) to 3 x Renogy 100AH LiFEPO4 batteries (260 usable) Here is the system on my 3GM30F powered boat. I’ll try to draw a diagram and upload it later. On the start battery side all is the same with a standard sealed FLA battery for start and leading to the old 1/2/Both/Off switch, the 94A alternator internal regulator takes its sense and excite from the common on the switch as before. The alternator output leads to a Victron Argofet isolator which keeps the battery banks isolated and allows charge to both banks.

On the house side, the batteries are paralleled and lead to a bus for charging and unswitched distribution this has the alternator current from the isolator, solar chargers, AC charger, and bilge pump. The Sterling external alternator regulator senses house voltage and provides control of the alternator to maximize house charging, provide alternator overheat protection (sensor on alternator case), and battery temp protection. A main on/off switch controls power to the switched bus which powers the main DC panel, second DC panel, and inverter with own disconnect switch and regular distribution from there to loads.

I already had the regulator and isolator installed as described so the batteries were essentially a drop in replacement. The internal BMS also provides protections to the battery. The starting battery provides protection to the alternator naturally in the event the BMS disconnects charging from the house batteries. I did have to change to serpentine belts with the conversion kit because the lithiums with external reg were too much for the v-belt to handle. Also, I have a disconnect switch on the external regulator to revert to sensing the almost always full start battery so to avoid robbing power from the engine when I might need all of the available power.

There are far more complicated ways to do it, but this is working well in my boat and cut overall battery weight by 1/3 to 1/2 and takes up the exact same space as the old AGMs.