Batts dead again??????

[Bill Lee]

I have a 42' power boat in the PNW plugged into shore power when I'm at the dock. We use the boat year round but in winter it's just for occasional "3 hour tours" and a couple overnighters. In summer, we're out for about 2 months and on the hook for the most part. We dock up every 5 days or so and plug into shore power for about 2 days. We don't have an inverter but have 2 refrigerators (one with a decent sized freezer). Despite using the genny daily for about 2 hours a day to charge up I have to replace the batts again. Port bank dead. I have 7 car type batts for the house bank (4 port and 3 starboard) which are also the engine start batts (I didn't design this). My batts have
Aged less than 3 years. I really don't want to run my genny more than 2-3 hours a day just because I'm not prepared to run it while I'm away from the boat and I don't want to be stuck on the boat that long during the day. I'm considering AGM batts but really don't know what I should get. Apart from halogen lighting at night, toilet flushes (4 a day) and water use (water pump) the refrigerators use less than 10 amps each cycling on/off. Any recommendations? Thanks and Cheers,
Bill

[Sailmonkey]

Car batteries....like starting batteries? If that's the case, you'll never get more life out of them. Best bet is to rip out the bunch of them and build a dedicated house bank of deep cycle or traction batteries.

[ShaunJ]

Have you tested the batteries yet?
What are the batteries rated at, how many Amp hours?
Are all the batteries the same size in each bank?

[Dockhead]

A few tips:

1. You will get better results with some kind of batteries designed for some kind of deep cycling. Car batteries are ill suited for use as boat house banks. Golf cart batteries, leisure batteries, true deep cycle batteries, there are many choices.

2. Put in a battery monitor and be aware of how deeply you are discharging your batts. It's better not to let them get below 50% before recharging. If you need more than 50% of your batteries' nominal capacity every day, then you should consider increasing the size of your house bank.

3. Make sure your genset is running a battery charger of adequate size, so that you are not putting unnecessary hours on the genset. Up to about 20% of your house bank's nominal capacity is ok for a battery charger.

On the hook, you will never get your batts up to 100%, as it is not reasonable to run your genset for the many hours needed to do that. So you will have less usable capacity -- from about 80% to about 50%. Might be another reason to increase the size of the house bank.

[Bash]

Replace those seven car batteries with a couple deep-cycle 4Ds.

[Florida Mike]

As said above you need to split the systems into two systems. A start system, and a house system. Depending on your engines starting needs if they are gasoline or small diesel powered select a group 31. For the House bank I would select 4, 6 V golf cart batteries in the series parallel configuration. Then add combiners to charge a house bank. Just my two cents, Mike.

[Mark1977]

Originally Posted by Bash

Replace those seven car batteries with a couple deep-cycle 4Ds.

Plus 1 on that.....get rid of the car bats...

[Bill Lee]

My diesels are pretty big - Volvo TAMD's 480 hp each. My mechanic was supposed to check out my batts but hasn't done so yet. I was wondering about AGM's for house batts because they can pretty well be flat lined (yes???) and then charge up quickly (yes???). But would I then need 2 chargers? One for engine batts and one for the house batts (AGM's)?
Cheers,
Bill

[NewMoon]

We've used AGM's both for starting our Volvo KAD44 diesel and for house bank for 11 years, so both our shore-powered charger and alternator regulator are set to AGM parameters for best results.

Figuring out your starting bank is pretty easy - how many CCA do the big Volvo's need? A pair of group 34's or group 31's will probably do. We use a pair of g34 AGM's, same as for the Cummins diesel in our truck.

Before you spend a ton of money on new batteries, wiring, etc. you really ought to calculate your amp-hour needs for the house bank. That depends on the electrical devices you use between charges, their current requirements, and how long each one will be running. A spreadsheet like Excel is great for this - it's an iterative estimating process. I could email the one we used.

Since you shouldn't go much below 50% and can't necessarily expect to recharge to much above 85% every day, you should have a house bank about 3X as big as the AH you require between charges.

AGM's are tolerant of somewhat deeper discharges than flooded, but they're not OK with taking them all the way down. I'd suggest no lower than down to 40%, or better no lower than 50%. The less you take them down the longer they'll last. Our just-replaced house bank (a pair of g31 Deka AGM's) lasted 11 years of cruising the PNW every summer, mostly anchoring overnight, with no generator.

AGM's also can sit for a very long time unused and not on a charger with little self-discharge. Many leave them untouched over the winter, even up in Alaska.

An amp-hour battery monitor is very helpful if you want to take good care of your house bank.

[Stu Jackson]

1. Totally agree about the car batteries. You might want to do some research on the basic different types of batteries for boat use. download the Ample Power Primer from Ample Power Company Home Page, and read West Marine's Advisor on battery types.

2. Before you jump on the AGM "bandwagon" (and there are folks who have them and love them, but they know how to treat them right), read theser:

AGM Battery Issues (from Maine Sail) [added 8/18/11]
AGM Batteries - Making The Choice - SailboatOwners.com

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries - SailboatOwners.com

[Florida Mike]

You can take this for what it’s worth. You are obviously not recharging your batteries in the two hours you run your generator. There are most probably multiple reasons, small battery chargers are the prime, whether they be AC driven and/or alternators on your main engines. I would recommend a house bank consisting of at least 4, 6 volt golf cart batteries. Starting batteries would be at least one group 31 per engine as close to the starter as physically possible and four simplicity sake is probably another 31 for the generator. There are all kinds of threads on here about different ways to hook up the charging system. Each one seems to have pros and cons. I personally would prefer to add two alternators one to each main engine dedicated to the house bank. Also increase your AC driven chargers or add another alternator to your generator if that is possible. I personally feel like battery chargers are a necessary evil especially on boats. You can always a the house bank size. The big advantage to the golf cart batteries is their size and weight as opposed to D4 or D8 batters. I have no experience with other than flooded cell batteries. Just my two cents, Mike.

[Bill Lee]

Thanks all. Yup, the batts are being replaced with high(est) amp Golf cart type. 2 extra on the port bank as we determined the wiring of the toilet, freezer, and water pump runs off port side. Too expensive to retire. Cheaper to add amps.
Cheers,
Bill

[bill good]

Just replaced my 3yrs old AGM with LIFEPO4. Have been thinking about if for years. The indications are they will have twice the life. I will be replacing all LA with this type from now on. (Read my update of today)

Regards Bill