Re: [Amel Yacht Owners] First Impressions: Firefly Batteries.

James Alton


   This is an interesting discussion,  I feel that I am learning a lot..the good the bad and the ugly….

   The batteries for the Maramu were installed in the engine room by Amel.  On the SM, the pass thru is wide enough to accommodate the batteries but I don’t think that this is possible on the Maramu due to space constraints.  In this location as you point out,  heat could be a significant factor in battery life.  (this is one of the reasons I installed an 8D Gel temporarily under the Vee bunk on the Port side.  The Gel battery is a very clean battery not requiring a battery box.)  I am considering future options to move the house batteries into the bow of the boat which would get them out of the heat of the engine room and also help trim the boat fore/aft.   The large draw items such as the thruster are in the bow so it seems like this might be something that could work…any input?  I am guessing (but do not know for sure) that since the degradation is a chemical process that the accelerated deterioration occurs only during the times that the engine is being used?   While damage was done during the heating periods, hopefully there is not ongoing damage when the engine room returns to ambient temperatures, so if this is correct unless one heats the engine room continuously for the life of the battery the life would not actually cut in half?    

    I have been reading that newer sealed  lead acid batteries used as starter batteries for cars are considerably more heat tolerant than those of the past.  The 2015 BCI Failure Mode Study reported an average life expectancy of 55 months under the hood and one additional year if the battery were kept in the trunk.  I don’t know if this benefit has been built into the batteries commonly used in our boats.

    Lead acid batteries are not too energy efficient so you might lose 15% of the power in charging the battery and if you discharge rapidly, you can lose up to 40%.  How much of that energy loss ends up as heat in the battery I wonder?  You make an interesting point about the Firefly batteries possibly running cooler due to the higher efficiency.  Again, it will certainly be interesting to hear your reports!   Thanks for sharing.


SV Sueno,
Maramu #220 


On Dec 14, 2017, at 7:12 PM, greatketch@... [amelyachtowners] <amelyachtowners@...> wrote:

Firefly specs the battery output up to as hot as 50C, but it does come with a caveat in their manual:

The optimum operating temperature for a lead-acid battery is 25°C (77°F). As a rule of thumb, every 8-10°C (14-18°F) rise in temperature will cut the battery life in half. 

That's a pretty standard rule of thumb that any chemist would use for a chemical reaction, and  I believe it is at least approximately true for all Lead-acid batteries.

Where Firefly might have a bit of an advantage is they have high charge efficiency, and very low internal resistance (specified as 4 milliohms) so they generate less internal heat during normal charge/discharge cycles.  They MIGHT run a little bit cooler in the same ambient environment than other valve regulated batteries.  On the other hand, a flooded cell that is generating gas will be losing a lot of heat that way, so I won't put money on it either way!

Bill Kinney
SM160, Harmonie
Fort Lauderdale, FL
Almost ready to be out sailing again!

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