Thanks Eric. That should inform folks who don’t understand the tradeoffs. My point is just that having more than a 500-1000 cycle battery charge life is great advertising, but is pretty useless for a seldom used boat. And given this infrequent usage, I personally cannot justify even buying new flooded PbA batteries, let alone AGM, let alone Lithium of any chemistry. My 6 used T105’s cost me $120 total…even though the really only deliver less than 100ah at this point, I expect they will last another 3 years at least and for me, this scenario cannot be beat.
Indeed everyone will weigh the tradeoffs differently…and should I personally get into a more financially stable situation, I might be tempted to add a string of Lithium to the boat.
It’s really great seeing so much more activity on this list these days with very very constructive and informative dialog. It truly helps to share your experiences out there so that new folks coming here realize that they’re not crazy after all in wanting to go electric.
Thank you all!
-Myles Twete, Moderator, Electric Boats
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Eric
Sent: Saturday, November 13, 2010 10:17 AM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Picking batteries
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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