Myles,
You make a good point. Once cycle life gets to be about 500 cycles, the chances of having the batteries expire from cycle age are pretty low for pleasure boaters like most of the people here. That said, I know that for many boaters (me included) FLA batteries often die with low cycle counts from mis-management. With their higher self-discharge rates, FLA batteries will sulfate if not kept on a consistant charging routine.
AGM batteries seem to survive inattention for longer periods without significant degradation.
Lithium batteries, LiFePO4 batteries specifically, have a much longer shelf life, and should be able to survive 6 months of sitting without any noticible loss of capacity.
Of course, with the considerable investment for any battery bank, having an automated charging system, either plugged in or renewable, will help any battery live closer to its potential.
So my takeaway from this is that cycle life is not as critical for most of our applications. Attributes like size, form, energy density, the ability to deliver more of the stored energy, and cost could be more important factors in choosing your battery bank.
======================================
Even though FLA are obviously cheaper than our other major battery types, I believe that they are least efficient for their size and weight. I find AGM to be a good compromise between cost and delivered energy. And finally, Lithium are half the volume and weight as either lead acid type and usually deliver more Wh per charge for the same Ah ratings, for a consdierably higher cost.
I have found that a rough rule of thumb is that AGM cost about twice as much as FLA for the same size, weight, and Ah rating. They will deliver more range in our typical use cases. Lithium batteries cost about 50% more than AGM for batteries that will deliver the same range, but are rated 20% lower in Ah, and are 60% smaller and lighter than AGM or FLA. This rough estimate includes BMS modules that will prevent any high or low voltage event and help keep the individual cells balanced with each other.
Everyone here gets to decide what is most important to them. I picked LiFePO4 batteries for many of the reasons listed above, but mostly size and weight. Cycle life was not a consideration.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Myles Twete" <matwete@...> wrote:
>
> Interesting note on cycle life.
>
> It would take me 150years to go thru 6000 charge/discharge cycles with my
> boat.
>
> Even if you were to use your boat every single day, it'd take over 15yrs to
> reach that cycle count.
>
> Not even the manufacturers of these batteries advertise them to last 15yrs,
> let alone 150yrs.
>
> Cycle life is meaningless to me and my boat except that if I were using
> Lithium cells, one overcharge or one over-discharge and the cycle life goes
> from awesome to pitiful.
>
> -Myles
>
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