I did a quick survey among boat owners here, did a few searches across the web, and spoke to a friend of mine who is an electrical engineer/Catalina 30T owner.
I finally made my decision based on a few things: a) my EE friend has AGM batteries and 2 solar panels. He told me that he consistently found that his lead-acids discharged faster than his AGMs, even with the same solar panels; he also said that while he had gone through pairs of lead-acids several times, each time lasting no longer than a year, he's now had his AGMs for 7 years.
At the time he was on a mooring as I was; now we're both on a new dock, so things will be a bit different.
I also based my decision on my own bad experience in the last year; I bought 2 "marine" batteries at $100+ each, and now one is bad already.
I'm also adding a small solar panel to my boat so that I can keep my AGMs topped off at the dock, without the need of a battery charger.
This seems to be a murky subject; on one sail forum (Sailnet I think), it seemed that AGMs clearly won the day, but here I'm seeing that there are lots of you who swear by lead-acids.
My final thought: If I can get 2 years at $500, that's the same as 4 lead-acids in 2 years, which is about what I've been through lately. I'm going to give this a try and heed my electrical engineer friend's advice.
You could buy those same Deka's at Sam's Club, as Duracell's, for $179.00 (below was the old price) and save even more...
My data is based mostly on mooring sailed or cruised boats but I do also have many at docks as well. At a dock or with solar I do see close to as long a life as 12V flooded (not 6V deep cycles) but not on moorings or on cruised boats..
Where does my thought process on this stem from? I am a marine electrician by trade and have invested in the very expensive equipment to capacity test, impedance test and track changes and determine "end of life". I began installing AGM's in boats when they were first marketed to the marine market. Back when they claimed 80% DOD was okay for them..
I also work very closely with a number of battery manufactures, industry leaders, the ABYC and I am heavily involved in the testing of new battery technologies not yet on the market to the public, including a new AGM variant current on my test bench. I don't just focus on lead aicd I also design & install both custom and factory made LiFePO4 lithium battery systems.
I can only offer my
real world experience across many hundreds of vessels. You certainly
can maximize the cycle life of AGM batteries but it can get expensive to do it right. I still install a LOT of AGM batteries but they are always installed and addressed as a compete system not just a drop in replacement for flooded batteries.
John Harries has written extensively about AGM's too:
Morgan's Cloud AGM's
Course you don't need to take my word for it. For the Deka/East Penn brand this is how they rate their
own batteries.
NOTE: Only ratings within a
brand/
manufacturer are useful. Cross brand cycle life data is useless because there is no industry standard for testing. Most all of them are
fantasy level data when applied to
real world marine use. Only in-house manufacturer testing across their own batteries can be compared for
guidelines.
-GEL Cycles to 50% = *1000 Cycles
-6V Flooded Golf Cart Batteries Cycled to 50% = *700-1000 Cycles
-12V Deep Cycle Flooded Cycled to 50% = *350 Cycles
-AGM Cycled to 50% = *300 Cycles
*NOTE: These are not what you will see in the "real world" except for the possibility of GEL.....
That is not my data but Deka's own data across their own batteries.... As can clearly be seen;
*They rate their 12V DC wets at 50 more cycles than AGM.
*They rate their 6V DC wets at 400 - 700 more cycles than AGM
*They rate GEL at 700 more cycles than AGM...
All batteries sulfate and one of the reasons AGM's suffer shorter life is because many brands can not be equalized. Lifeline's can be, but Deka can not.
One needs to be very careful when comparing batteries to other batteries. Many flooded batteries are sold and RELABELED by
regional distributors and may not be what they claim to be. I see this very often. Compare a factory branded battery like a Trojan, Crown, US Battery or Deka to a factory branded AGM and then you have a much fairer comparison.
I have seen plenty of starting batteries "labeled" as "deep cycle" by
battery distributors so it is buyer beware when buying non factory labeld "distributed" branded batteries.
1 year life to 7 tells me something changed dramatically with the switch from flooded to AGM.
For your Deka's:
*Set your charger at EXACTLY what Deka wants to see - 14.4V / 13.4V (optimum @ 75F)
*Make sure ALL charge sources including solar are accurately temperature compensated
*Make sure your alternator can handle the acceptance rate of the AGM batteries
*Try to feed them at least .2C in charge current from the alt or shore charger
*Get back to 100% SOC as often as possible - 1 timer per week minimum
*Be sure your charger is charging to full - Less than 1% CAR at 14.4V = 100% SOC
*Use a smart (truly smart not just in label) battery charger
*Keep them out of engine spaces or areas where it routinely gets above 80F
*Do not routinely discharge below 50% SOC
*Try to get back above 80% SOC ASAP after each discharge then 100% soon after
* Break your batteries in - Discharge then recharge to 100% every time, 20+ cycles.
*Install a battery SOC meter such as the Balmar Smart Gauge
*Shallower discharges lead to longer cycle life, don't go to 50% unless you
need to
Do the above and you will maximize what you can get out of those batteries.
