E38 Battery Replacement - deep cycle or dual purpose?

[Dan W]

Hello - I was hoping to tap the forum again for a little guidance. I've decided to replace the 3- group 31 batteries on Magellanes this spring... boat is wired with a house bank (2 batteries) and a separate switch for the engine battery. All 3 can be paralleled together.

The batteries on the boat now have lasted 7 seasons - they are "Seahawk" marine batteries, straight deep cycle batteries -- all batteries are the same. I'm inclined to follow the mantra of "if it ain't broke, don't fix it" and go with same set up -- however I can only find "dual purpose" batteries from the same manufacturer locally (after getting 7 seasons I am "brand loyal").

The "ratings" on the dual purpose seem very similar, cranking amps are about 8% higher on the dual purpose (875a vs 810a), Average minutes @23 amps is about 10% less (205a vs 225a).

Being that they are the same brand, similar ratings, I'm inclined to go with the Dual Purpose --- however I have heard that dual purpose can "fail" all of sudden vs deep cycle.

Any thought opinions and experience from the forum would be appreciated.

Thanks,

Dan

 

[rwthomas1]

The way I understand it, deep cycle is a specific way of building a battery to deliver a moderate amount of current over a long period of time while withstanding multiple discharge cycles. Think golf cart batteries. A starting battery is made differently, to deliver maximum current for a very short period of time to start an engine, then get recharged quickly. It would seem that a dual-purpose battery is a compromise that likely does neither well but "good enough".

With three batteries on board you have the ability to dedicate a start battery and have two as the house bank. So why not? I have heard that there are only three or four battery manufacturers and they make them all to whatever specs the "brand" asks for.

My E38 came with Napa Commercial deep cycles, three of them, 2 house and 1 start. I reconfigured the battery box to make the three batteries into a single house bank and added a fourth battery, from Interstate, as a start. I am quite sure the Napa's are nearing the end of their life as they are dated '00. Thats NINE years. But they don't get used very heavily, are well maintained and always charged. I'm not going far, have a generator, etc. so I am not too concerned. When they give any indication of dying I'll just replace them. Quite likely I will go with Trojan as I have never heard a bad thing about them and they are reasonably priced.

RT

 

[Maine Sail]

Deep cycles

Deep cycle batteries will last longer as they have thicker plates and are designed for more discharge cycles. You really do not need to worry about CCA or MCA on a small diesel as even a PWC battery will start most of them if you needed to. My 44hp Westerbeke four cylinder only draws roughly 165 peak amps at start up and even then that is for a split second. 810 MCA is about 6 times more than I'd need..

 

[ted_reshetiloff]

According to Universal you need min of 400cca for the starting battery.They reccomend 400-700 for the 5432. I just replaced mine this weekend with a group 27. I have been using 2 group 31's for the house bank and a group 27 for the start for 5 years. They are all Gels. The house bank is 9 years old and both batteries tested out at 790cca each which means they are still in great shape after 9 years. The starting battery was 12 years old and finally gave up the ghost this spring(tested at 185cca). I charge the start battery with a Xantrex Digital Echo charge. Basically a smart combiner. Alternator output directly to house bank with blue seas panel to emergency parallel all three.

Gels are more expensive, I paid $190 for the group 27, but they dont off gas and if you dont run them below 50% they will last a long long time. Lead acid batteries scare me. I delivered a bendytoe 46 down from Long Island last summer that had 3" of standing battery acid in the battery well from boiling over I suppose. Owner thought it was water and burnt the hell out of his hand cleaning up the mess. Obviously AGMs are probababy the best but hard to justify expensewise IMHO unless you are living aboard and doing serious cruising. I guess the same can be said about gels too, I just hate battery acid. Stuff freaks me out...

 

[Tom Metzger]

I delivered a bendytoe 46 down from Long Island last summer that had 3" of standing battery acid in the battery well from boiling over I suppose. Owner thought it was water and burnt the hell out of his hand cleaning up the mess. ...

When you overcharge (boil) a flooded cell battery you give off gas, hydrogen & oxygen. It is the water being broken down. Three inches of acid in the battery box indicates that he had a broken case, most likely from freezing the battery.

Buying an over sized battery will extend the life as you define failure as a smaller percentage of the rating. People who want reliability buy the correct size and replace it more frequently, before it fails. Testing does not cover all failure modes.

 

[u079721]

I too would suggest that you get true deep discharge batteries for your house bank. On our E38 that was two Trojan Group 31 batteries wired in parallel. For the third battery I bought either a dual purpose or a starting battery (I forget which), but never used it and kept it in reserve as an emergency back up. I found it simplier just to always start the engine on the house bank and leave it there.

 

[ted_reshetiloff]

Had not thought about the cracked battery case. Funny thing was all the batteries in that boat were in good shape. I think thats why the owner thought the liquid was just water from a leak someplace. Ive seen some crazy stuff on boats so it would not surprize me if someone replaced a busted battery without cleaning up the spilled acid. Eeeks just thinking bout that stuff freaks me out...

As for appropriate starting battery for the E 38 I would again reference the engine manufacturers reccommendations for 400-700cca. A group 27 would fit the bill there but so would a 31. Not sure where you put the 31 though. Mine are under the strbd setee and there is barely room for the 27 in the middle compartment. The 2 31's for the house bank are in the aft most compartment of the strbd setee. I suppose you could put it in the cockpit locker in a box there but then you have to rewire probably.

 

[Steve]

More power

We did some crazy stuff because the Admiral kept asking (demanding) for more power... !

Steve e35-3 #159

 

[Captron]

Go for Gels

You need to go with true deep cycle batteries for the house bank.

I have two Gel cells for our house bank and a third small one (Group 24 I think) for a starting battery. The house bank batteries measure about 13x13x9.5 so I'm not sure what size they are ... I thought they were Group 31s but the size doesn't sync with the catalog sizes for G31 ... so who knows? Mine are Prevailer brand (German manufacture I think).

Anyway just happened to be thinking that maybe it was time to replace mine even though they still function like new. I poked around and found a tag on one that had the date punched out ... March 2000. Hmmmm. I think I'll wait to replace them just to see how far they'll go. But after 10 years, they start to get very cheap. High initial cost maybe but when they last like that they're a bargain.

Probably the cheapest way out (Initial cost anyway) is to use a pair of golf cart batteries wired in series. (6v + 6v = 12v) ... Sam's club had them for $72 ea. the other day. They should last close to 700 cycles with good maintenance ... mainly checking the water and keeping the terminals clean. They also had an 8D, same capacity as two golf cart batteries (220 amp hours) for $179. I would prefer the golf cart type though since the 8D weighs over 150 lbs and my back has it's limits.

The beauty of gels is they don't need much maintenance just make sure the charging voltage stays under 14.1 ...

Also I've seen my battery monitor register 65 amps initial charging rate. Assuming my bank is 200 amp hours or so, that's almost 33% of capacity. Maybe they'd take more but my alternator specs say it's a 60 amp unit so the alternator may be the limiting factor. That means I can bulk charge the gels faster than wet cells that will only accept maybe 20% of capacity. AGMS supposedly can take up to 50% of capacity so consider charging time if that's important to you.

Also for what it's worth, I noticed that West now shows an alcohol charged fuel cell in their catalog. The jury's still out on that rather expensive option however. It's coming though. The times they are a changin'. Oops, dated myself.

 

[ted_reshetiloff]

Gotta agree with Ron on the Gels. My house bank is from 2000. My electrical guy has this cool battery tester that instead of being a load tester it can tell you how many CCA the battery has in it. You compare that with what it should have when new and can get an idea of how healthy the battery is. Im sure it does more than just that but when he tested my two group 31's they boat came out just under 800cca which is what they should be when new. Ron's right they are a higher initial investment but if you treat them right they hold up well, certainly longer than any wet cell I know of. He's also right about the rate of charge they will take. This means much less engine time to charge the bank. Obviously the AGM's are sweet but at those prices I think I need to live aboad and be doing some serious cruising to justify that .