Battery question

[forbes210]

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.

[Phillbo]

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.

[forbes210]

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.

[biggerseagar]

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.

[mmwjr]

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

[biggerseagar]

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.

[Kevlar7r]

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.

[biggerseagar]

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?

[mmwjr]

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.

[shrew]

^^^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.

[forbes210]

Thanks for all advices. I had to removed my batteries for winter since I can't charge/maintain them at the place where I store the boat. I'm keeping them home and will connect the charger every month or so. In this case I think I will get one deep cycle battery with enough cranking power and see how it will work for me. I can keep the other starting battery for now. Ideally I'll be using only deep cycle battery and will keep starting battery only as a back up in case my deep cycle will be to weak to start the boat.

[Phillbo]

Not sure if you mentioned the engine but the Volvo does not like to be started on a weak deep cycle. Best to just get in the habit of always using a fresh starting battery to start each time. Thats what I do.

Start using the starting battery and charge BOTH while underway.

[forbes210]

Phillbo its a merc 5.7. I might do as you advised in case deep cycle will not work well with starter and be using starting battery to start and deep cycle while on anchor etc. I'll have to put switch in BOTH position to charge both batteries and I've read few times that this is not recommended. Not sure if it applies only when starting the boat or in general.

[Phillbo]

I don't think it's the starter that is at issue but the ECM.... I've NEVER had my switch on BOTH ...


Again, here is how mine is set up and it works great. I do boat on Lake Powell so a day of cruising can be 4 hours of engine run time easy.

........................


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.

[forbes210]

Phillbo. My charge won't charge both batteries from alternator when in 1 or 2 position. It will only charge both batteries from alternator when in BOTH position. At least thats what my manual says.