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Old 01-24-2015, 10:06 PM   #1
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Hi All,

Recently I removed the battery for winter and while charging them home noticed that one of them didn't want to take a full charge. I'm not surprised since I stayed overnight few time in one marina which didn't have a shore power and exhausted this battery with refrigerator etc to the point that I couldn't start the engine. In my Maxum 2500 I got 2 batteries with switch which means that one battery serves as a house and starting battery and the other is just the back up. I wanted to buy new battery and was thinking about AGM since it will work better as a deep cycle battery (especially with new stereo which draws some power while on anchor). Do I have to look at anything before I will AGM battery? One guy told me that I need to match it to my alternator and battery charger since AGM is a different technology and could damage them. Also is it ok to replace only one battery with very good one like AGM which I could use all the time and keep my good current battery as a back up battery? I'm attaching image of alternator sticker and battery charger. Thanks in advance.
IMG_20150119_132829.jpgIMG_20150119_132847.jpg
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Old 01-24-2015, 10:53 PM   #2
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First of all you are using your batteries incorrectly. One should be a Starting battery and the other should be Deep Cycle battery for the house.

My set up is like this:

Batt 1 - Starting Battery
Batt 2 - Deep Cycle House Battery.

I place my switch on position 1 to start and leave it there while cruising around during the day (both batteries are being charged by the alternator.
I move the switch to position 2 once I am on the hook and let the deep cycle house battery power everything for the night.

I don't think your charger will be able to accept one AGM and one wet cell battery. I'd replace them both and start fresh with either type you choose.
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Old 01-25-2015, 12:21 AM   #3
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Thanks for advice, I didn't think about it before. When I bought my boat 2 years ago it came with 2 starting batteries so it doesn't really make sense to switch in between of them when staying on anchor etc. I believe my boat when running is charging only battery to which is switched and when plugged in to shore power then it charges both. Probably I would rather to get 2 either dual purpose batteries and don't switch between of them or get 2 deep cycle batteries with enough cranking power. I'm not sure if my charger will work with AGM batteries (both AGM) since it says on it lead acid/gel cell.
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Old 01-25-2015, 12:28 AM   #4
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It is a known fact that agm batteries still are more expensive than they are worth. You get more bang for your buck with a wet cell battery.

Buy a deep cycle battery, group 29 or 31 where your amp hours rating is around 800. Or if your need more and have room wire up a second house battery to double your amp hours.

I believe your charger is a three bank so if you went with 2 house and 1 starting you could charge all 3. Imho.

Why do you take your battery's out? I have a 3000 and leave it plugged to my shore power to charge all winter long. Last set of batteries lasted 5 years for me. Something to think about. Make sure your water is topped off and that they are charged ( use a multi meter to check) 100%. I quit hauling batteries out of my boat many years ago.

That is my 2 cents.
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Old 01-25-2015, 12:45 AM   #5
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So both current batteries are starting ones correct?

If yes then when you did a deep discharge of the one it was slightly damaged hence the reason for it not to fully charge.

As Roger said get two large deep cycle batteries.

PS I remove mine for the winter as I am in a boatal and do not have the option to plug the charger in. Instead I take them home and but them on a trickle charge for one week each month
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Old 01-25-2015, 01:12 AM   #6
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Forbes....there is no such thing as a dual purpose battery. This is no more than a marketing ploy from the battery industry. You can use a deep cycle as a starting battery as long as they amp hour rating is big enough. However you don't want to use long term a starting battery in a deep cycle situation.You would be throwing your hard earned money away. One or the other as Philbo has stated.
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Old 01-25-2015, 07:02 PM   #7
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I just recently purchased a group 31 agm for my house battery (which on the 3000 is also the port starting battery).



I have been very happy with it. At the New Years party, all the lights were on, stereo on, water system on, fridge on till 3am. I would have had to start my generator by then on my old battery.



Yes, they are expensive, but I am terrible about keeping my batteries full of water, so I like the sealed aspect.



An AGM is still a lead acid battery, no different in chemistry than a flooded battery. The difference is how the lead is contained. Rather an a thin lead plate, it is a fiberglass matt with the lead adsorbed on it. This is stronger than a thin lead plate, and can handle the heat of rapid and deep discharging and charging without warping.



I've only had it for a few months, but so far I'm very happy with it.



Oh, I've also noticed, it seems to stay cleaner than a traditional battery.
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Old 01-25-2015, 08:46 PM   #8
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The deal with agm batteries is that they can handle abnormal vibration and because the inside is a paste and they are sealed and not a liquid inside, these batteries can mounted upside down. Cost is also almost twice as much as a wet cell battery. Now if you need all this the agm battery is a great way to go. Another plus is that their rate of losing it's charge is minimal compared to the wet cell on a monthly bases.

So is all this worth it?
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Old 01-25-2015, 08:53 PM   #9
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Not an expert but from what I read the AGM needs a battery charger designed for then as the standard flooded charger can damage them. Try googling for more information.
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Old 01-26-2015, 01:51 PM   #10
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^^^Correct^^^^

I have the following:

Leg 1 -Starting: 1 x AGM Starting battery (Group 27)
Leg 2- House: 2 x AGM Deep Cycle (Group 31)

2 bank isolator switch

I have a 3 bank charger with setting for 'Flooded', 'Gel', 'AGM'. 2 bank isolator switch. I start and run on 1 and sit on 2. I do spend a lot of money for Lifeline AGM batteries. I like their ability to drawn down deeply. very slow discharge over time. Shock absortion. I leave them in the boat and don't bother to trickle charge them in the winter. In the spring, the first thing I do is turn the stereo on.
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