Battery Charging

H

HarlenW

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25699
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I have a bank of 5 AGM batteries with a total rating of 580 Ah. When at my slip and connected to a battery charger, once fully charged, how much should they discharge under the maintenance load to then begin recharging? I believe this is called the "refloat set point" but am no expert.

I understand that it is good for the batteries for them to discharge some and then recharge fully on a regular basis.

Thanks!
 
I left my battery charger on 24/7 while in the slip. Usually got 6-7 years of life out of my batts. Used ACDelco Voyager batts, maintenance free. Left on boat during winter storage. Would go down every 4-5 weeks & plug in charger for an hour or so.

BOB J
 
Should not need to do that with AGMs.
 
Gee Bee, are you directing that to me or HarlenW ? In all the years I owned a boat(3); never had more than 1 battery per engine. never had a problem. Can't believe some of these Captains carrying 500# of batteries around. It's their choice !
 
Not trying to hijack this thread....
Is ther a way I can determine what battery type my charger is set up to charge? AGM, Gel, flooded?
The switch is on the back of my charger and there is no way in hell I can get to my charger, and unmount it from the bulkhead to look at it.
My boat has AGM's but I can't assume the charger is set up correctly to charge them. According to the manual, the charger comes from the factory to charge gel batteries. Could that be considered a universal charge and ok to charge flooded and AGM as well?
 
Since you have the Manual; call the mfg. give them the info. Model # etc. and ask customer support what you want to know.

BOB J
 
It isn't a universal charge. Flooded lead cell and AGM have similar (though not identical) charge profiles as they are both "lead acid". An AGM setting should be fine for both. Gel cell is a different animal - sulfuric acid mixed with a silica gel. It has a unique charge profile.

My .02
 
Originally posted by JoLin

It isn't a universal charge. Flooded lead cell and AGM have similar (though not identical) charge profiles as they are both "lead acid". An AGM setting should be fine for both. Gel cell is a different animal - sulfuric acid mixed with a silica gel. It has a unique charge profile.

My .02
[/quote

Actually, I saw some technical info on battery charging and gel is inbetween flooded and AGM
Click to expand...
 
Actually, I saw some technical info on battery charging and gel is inbetween flooded and AGM
[/quote]
I think you're referring to the 'float' charge, and that's only one concern. The OP's charger, which has settings for each battery type, is a 3-stage charger. In the initial stage, known as the "bulk" phase, the charger set to Flooded or AGM will output higher voltage than when set to Gel. The same holds true for the "absorption" and "float" stages.

The potential issues I see are that if the charger is set to Gel, flooded and AGM batteries might not receive a full charge. If the batteries are Gel cell and the charger is set to flooded or AGM, the gel battery might be damaged from overcharging.

My .02
 
When I bought current my boat, the PO had 31D Sears AGM's. I got 3 yrs out of them based on the date stamp on the batteries. I replaced them with new 31D Sears AGM's figuring maybe he knew better than me and only got another 3 yrs out of them. Also, my Sears Diehard Group 27 flooded cell battery for my generator boiled off the electrolyte within the first year. I have a Pro-Mariner charger circa 1989. On my previous boat, I bought NAPA truck/bus flooded cell batteries and always got 5-6 yrs. out of them. I just bought Sam's Club 31M Duracell made by Deka (flooded cell batteries) for $75 each vs. the $299 Sears AGM's. My unedumicated theory is that AGM/s and flooded cell batteries do not play well together with the same charger-at least with the older (much older) battery charger technology. I had a Guest Smart Charger on my previous boat and maybe that was the reason for the longevity of my battery life? Just thought I'd throw out my experience-your results may vary and I'd be happy to hear other's opinions.
 
The problem with AGM's is that once they get completely - or near completely discharged - they're never the same again. Optimas were all the fad for a bit - and they ARE really good batteries if you take care of them, but they do NOT suffer any abuse at all.

Conversely, I've got 7-10 year old conventional batteries in both my camper and boat that get put on a good charger anywhere from a few times a year to every few years, topped up with distilled water if I happen to have an open jug of it in plain view and arms reach when I throw them on the charger in the garage. They sit outside in the winter, in plastic battery boxes in the boat and in the camper. If it's nice out and I'm bored they might get topped up with a trickle charger, but for the most part I ignore them until I think I might need them. Mfr. date on the camper battery is 2011 and the boat battery is at LEAST a couple years older, and through all the abuse I have no problems with them. Camper battery will power lights, stereo, heater/hot water control for at least 4 days. Try that with an AGM and you'll need a new one each season (which you WILL get better performance out of until you neglect it).
 
I believe it is good practice to keep all technologies of batteries, including AGMs, fully charged when not in use. I have AGMs and keep them topped off with a solar trickle charger when not in use.

Roy
 
My AGM's never ever came even close to a major discharge. Maximum time on the hook was maybe 5 hours running only a cheap stereo-no sub-woofer or amp, vhf radio on and running the bilge fans for a couple of hours after setting the hook to pull the heat out of the engine room. I always started the engines prior to using the windlass and always plugged into shore power and the charger when at the slip. I do notice that after switching to the Duracell 31m's, the engines do not crank over with the same gusto.
 
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