Hi Myles,
I can't stress enough that all charging sources should be regulated appropriately for the battery chemistry. All battery, charger and regulator manufacturers mention the importance of this. AGM and Gel cells should never see volatages higher than 2.4-2.45V per cell (14.4-14.7V for a 12V battery). Simple FLA battery chargers will often run above 15V, which can damage AGM or Gel cells.
I agree that undercharging is the leading cause of premature death for lead-acid batteries, AGM or FLA. My house batteries would die from sitting too long below 12.2V and sulfating. The problem was when the boat would sit too long unattended. FLA batteries self-discharge at 3-4% per week, which means that if left alone for 4 months, my fully charged battery would be around 60% discharged. AGMs have a self-discharge rate of 1-3% per month, which mean that the same 4 months would leave the batteries less than 15% discharged.
Of course, if one keeps a maintenance charger on their batteries, self-discharge isn't really an issue as long as it is regulated to the proper voltage.
These are all things to keep in mind. (Who knew that batteries were so complicated?) They're not really, but they all have specific attributes that make it difficult to say which type is "best". Like everything thing else, the answer is "it depends".
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Myles Twete" <matwete@...> wrote:
>
> Ø People also recognize that AGMs seem to last longer in the real world and
> now the AGMs are cheaper in the long run.
>
>
>
> It deserves mention that one of the most significant factors that kills AGM
> batteries but is generally not an issue with flooded batteries is
> intolerance and inability to recover electrolyte capacity after excessive
> overcharging. Most AGM batteries do not provide a way for the end user to
> rehydrate cells after they have "vented". The only ones I have ever seen
> that do offer this capability are the Hawkers, which have snap-off tops,
> with rubber caps on tiny cell access ports. It is fairly easy to rehydrate
> over-charged, vented cells in a Hawker AGM. This is not the case at all
> with the Optima AGM batteries…
>
>
>
> Given that, many people have `killed' their pack of AGM batteries well
> before they delivered the expected cycle life. This is particularly the
> case for those who didn't invest in a BMS, but even with a quality BMS, the
> AGM still suffers from undercharging effects as with floodies, yet they
> cannot tolerate much in the way of an equalization charge to reverse the
> sulfation effects.
>
>
>
>
>
> From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
> On Behalf Of Eric
> Sent: Monday, November 14, 2011 10:22 AM
> To: electricboats@yahoogroups.com
> Subject: [Electric Boats] Re: Where to even start
>
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