19 posts / 0 new
Last post
McFly
Offline
Joined: 10/22/18
Posts: 190
4x 6V Batteries.....vs. 2x 12v 4D Batteries

Hey folks.  I'm getting ready to rebuild my house bank, which consisted of 2x 4D 12v batteries.  I will also be adding a pair of 110w solar panels and an MPPT solar controller to the mix as well.  I was considering using 4x 6v batteries, wired in series/parallel.  My chief motivation for this would be ease of handling, the 4Ds weigh in at 115# each, the 6v weigh half that.  The downside is they cost twice as much!  

Has anyone used 6v batteries?  I have yet to find any that are made specifically for marine use, they tend to be for golf cart and RV.  Wondering what your recomendations are.... 

Thanks!

Mike

Jackfish Girl, 1999, C36 MKII, Tall Rig, Wing Keel, In-mast furling, Phinneys Harbor, Bourne, MA

Windhover
Offline
Joined: 7/29/18
Posts: 3

I'm considering the same thing.  All roads seem to lead to Trojan T105 as the best option for long lasting flooded.  Best budget option seems to be Costco.  Youtube and Sailnet.com have loads of good info.  What is good for an R/V seems to be just as good for sailing, except that sealed seem to do better if they get knocked over :)

 

Then of course, there is Battle Born Lithium Ion if you have the solar panals and the buget.

dpower
Offline
Joined: 6/20/08
Posts: 189

I made this decision years ago.  Our boat came with 2 Interstate 4Ds.  After learning about our electrical needs and checking both this forum and the original email list, we changed over to the Trojan 105+.  Using a Link 10 battery monitor and regular maintenance, we got 7 years before I began to question their performance.  I also have two 95 watt flexible solar panels on the bimini.  They are not quite enough but extend our days on anchor so no need to run the motor or our Honda. When you get the Trojans, just make sure the battery terminals are compatible with wiring terminals.

mogline's picture
mogline
Offline
Joined: 1/5/08
Posts: 47

Change to four 6 volt (golf cart) batteries.  These are not only a lot easier to handle, they are also true "deep cycle" batteries.  Most of the 4Ds you are likely to find will be starting batteries intended for trucks and busses even if labeled as "dual purpose."  There are some instal issues to be aware of.  On  our 2000 MkII the fiberglass battery boxes were a little too short to hold the 6 volts.  We solved this by cutting each box in half and then fiberglassing back together so that they were about an inch longer (barely fit into the space under the seat but now each box holds two 6 volt batteries.  You also need to pay attention to the height of the batteries.  There isn't much room to the top of the battery compartment.  I could not fit T105s, but found that the Duracells made by East Penn fit easily.  Better news about the Duracells is that they can be purchased for very little at discounters like Sams Club or Batteries +.  They can be had in either 215 AH or for a little more 235 AH.  My first set of these lasted for 7 years and I only replaced them with new Duracells last year before we headed to the Bahamas for the winter. I assumed that after 7 years of use they probably had a lot less than there original capacity left.  Other than the VacuFlush this is the best change we have made to Shadow.

McFly
Offline
Joined: 10/22/18
Posts: 190

I should have updated sooner, but your mod to the battery boxes inspired me. After buying the 4 Trojan T105s, I too cut the original boxes in half and extended them by about an inch with fiberglass.  Thanks for that tip!

Mike

dpower
Offline
Joined: 6/20/08
Posts: 189

You should measure for height clearance. We had no problems with the clearance of the Trojans.  We did not use the original battery trays.  Instead, we used separate battery boxes, one for each battery.

McFly
Offline
Joined: 10/22/18
Posts: 190

The T105s are a bit taller.  This meant getting rid of the old 2x4s that were toed in as hold-down straps across the old 4Ds, I assume this was the original factory arrangement.  Instead I added SS footman straps to the base, one to stbd and one toward centerline for each pair, and then ran nylon straps beneath the battery boxes, through the SS footman straps, and up and over the batteries, cinching them down safely.  It also makes it much easier to check the water quantity of each battery cell.  

I have used Strapworks.com for new bimini straps and these battery straps. You can pretty much make ANY strap you can dream up with these guys, and for low $.  I can't recommend them enough.  Shameless plug:  ​https://www.strapworks.com/default.asp

 

Paul Revere
Offline
Joined: 3/30/19
Posts: 30

We put 4 6volts in for the house bank on our mark 1. It's a tight fit but having 470ah compared to the 300ah at best you would get with 2 12v 4Ds is great. We put the starter battery under the. forward seat. The 6vs we got were Duracell 235ah from battery plus.
you remove the battery box(its just glued in on the mark 1, so just heat it with a heat gun) and have to cut a small notch to make the opening a little wider to fit them.

McFly
Offline
Joined: 10/22/18
Posts: 190

Thanks so much for the advice.... yet again.  My house bank sits under the fwd facing seat on the stbd side (cranking battery under the aft facing seat).  At first glance of the specs, it seemed that the Trojan T-105s were only just slightly taller at 10.875" vs what I have in there now, Interstate SRM-4D at 10 3/8", which is a 1/2" difference.  So I'll have to make sure I can spare the 1/2" of clearance.  Otherwise, it seems the footprint is about the same as the 4Ds.  

Is this the Trojan to get?  ​https://www.solar-electric.com/trt16vo225ah1.html

Is this the Duracell folks are talking about?  https://www.batteriesplus.com/productdetails/SLIGC115?storecode=772&locationofinterest=9001915&locationphysical=9002048&utm_source=google&utm_medium=shopping&utm_campaign=ecommpla&gclid=Cj0KCQiAm4TyBRDgARIsAOU75spGPtuO20l0SqN5z6JPfyviqDJ8Dd51lBDqkbYNdSpjMNNHo7-PxIQaAjdxEALw_wcB
 

Thanks again for all the help folks!

Mike

Paul Revere
Offline
Joined: 3/30/19
Posts: 30

Yes those are the Duracell I got

Chachere's picture
Chachere
Offline
Joined: 10/27/10
Posts: 674

Interstate has a variety of deep cycle 6V golf cart batteries, and probably lots of dealers in your area. We've had 6 seasons thus far with the current set, which I believe is model 2300UT, rated at 242 AH, and which according to Interstate's website has a suggested retail of $168 each, and measures  (11.25" high by 10.25"w x 7.125"d). May also be known as the US Battery model US125XC2, for which the spec sheet is here.  I've been told that all of these are actually rebranded batteries made by Deka/East Penn

We have just one pair (giving us a house bank of 242AH @ 12V), but with solar panels we've never found a need to expand to more capacity for cruising, even though we run the refrigerator and other power users (we have a decent battery monitor and can see that we never drop below 70% charge), and have only the stock alternator.
 

Zefyros
Offline
Joined: 5/8/15
Posts: 11

Hi Mike,

I have the exact same setup as your plan, with Trojans.

Check your local suppliers. I got a great deal in Venice on mine.

I love it.

I check the Batt water level every month, and I refill as needed.

Great batteries and much easier to haull from the car to the Batt well.

With all the lights being LED, I have no power issues with a weekend in Catalina, even with the fridge, the esspresso machine and the ice maker.

Zefyros
Offline
Joined: 5/8/15
Posts: 11

Go for it.

two-rocks
Offline
Joined: 8/11/17
Posts: 67

Several CANE (Catalina association of New England) members here in the northeast have 6v golf cart batteries and work great. I put them in my last boat. The best value seem to be the Duracell rebranded. Interstates are hit or miss. Trojans are very good, but not enough volume here (golfing all year) to find the pricing FL people report. 

Now for the counter point. I plan on going with lithium, but can be more complex. My main reason has do do with usable capacity as well as system efficiency. You loose about 15% on the round trip path of electricity charging lead acid. Only using solar (as we do), it's the equivalent of upsizing our panels by 15%. But it gets better, the charge profiles of lithium are nearly flat - and accept almost all you can throw at them until full. No multi stage, no taper current, etc. But wait, there's more...partial state of charge is no problem for lithium, no so with lead acid.  

The other reason is usable capacity. With lead acid, to maintain the longevity of the batteries, only cycle to 50%. Deeper cycling shortens the life exponentially.

The cost/benefit for golf cart batteries is hard to beat. The system benefits to lithium is hard to beat, although most people don't keep the boat long enough for lithium payback.

 

 

 

Chachere's picture
Chachere
Offline
Joined: 10/27/10
Posts: 674

There are tons of discussions and opinions to be found on the web, such as Cruisers Forum and Sailnet; suffice it to say that Li batteries do not appear to be a simple matter. 
 
Former C36 owner and boat tech guru extraordinaire Rodd Collins ("Mainesail") has an extremely detailed (of course!) writeup on his webpage here:
https://marinehowto.com/lifepo4-batteries-on-boats/    where he makes this explcity warning "I do not believe LiFePO4 is ready for mass DIY prime time builds."   Having slogged through most of that article, I would tend to agree, but it sure looks promising (at some point, at least!).   I'm not jumping on this as a house bank for our boat for the time being (although I've been mightily impressed with the LiFePO4 battery on our Torqeedo outboard),  since I've found our existing 6V lead-acid golf cart batteries totally meet our needs while cruising, but long-term I can see going this way once most of the kinks of this new technology are worked out (hopefully by someone other than us!)
 

Mainesail nicely expands on the advantage that Two-Rocks asserts, thus::
"GET OUT THE DEAD LEAD:
The term “dead lead” is s term I coined in my electrical seminars. The typical lead acid bank consists of 65-70% of the weight being comprised of “dead lead” or the excess lead you carry around but that you can not use. If you have a usable capacity of just 30-35% of the bank, when out cruising, this means that you are carrying around 65-70% of that weight in unusable “dead lead” capacity. This 400Ah LFP bank weighs 130 pounds & 80% of it is fully usable. This means just 20% of it not actively usable or you simply don’t want to use it for optimal cycle longevity. As a result, we carry around a measly 26 pounds of unusable battery on our 36 footer.

Lets go back to usable capacity for a moment. If I wanted to equal the usable capacity of this 400Ah LFP bank in lead, I would need the equivalent of 8 GC2 6V golf cart batteries or approx 900Ah’s. 35% of 900Ah is a usable capacity of 315Ah’s. 80% of the 400Ah LFP bank is a usable capacity or 320 Ah’s. A 900Ah lead acid bank weighs 520 pounds. If I used just 35% of that bank, as I would when out cruising, then I would be hauling around 338 pounds of “dead lead” or 338 pounds of unusable Ah capacity. Twenty six pounds of unused LFP or 338 pounds of “dead lead“..?? Points to ponder. Again, if you have a large PV system or ample alternative energy systems then you can use more of the lead bank in daily cycling. On our boat, and many like it, this was not an option without making her look like a clown car of solar. My wife put her foot down on more solar many years ago and can’t even stand the look of the moderate PV system we have now."

motarded421
Offline
Joined: 4/20/18
Posts: 40

I'm not sure if you've made your purchase yet, but I'm redoing the entire electrical system on my Mk1. I'm opting for 2, maybe 3 LiFEPo4 batteries from Battleborn. The cost is insane compared to other options, but the life exectancy is also 3-4x what you get from flooded batteries. The weight is amazing too. I can't wait to get these installed later this month. 

McFly
Offline
Joined: 10/22/18
Posts: 190

I ended up going with the 4x Trojan T105 6v batteries.  Modified the battery boxes to get them in side by side, added new nylon straps as hold-downs and I'm running 2x 110w solar panels, mounted on the bimini, into a Victron 75/15 MPPT controller to the batteries.  I mounted the MPPT under the nav table with the chair removed. What confused me is that it mattered which POS terminal I selected to bring the power from the MPPT to the bank.  Initially I just brought the lead to the closest pos terminal (most aft, stbd battery + term).  But that only resulted in charging HALF the bank, and showed 6+ volts on the app and confirmed on the victron battery monitor as well.  Moving the lead to the other side of the bank resulted in 12+ volts (my four 6v batteries are wired in series-parallel).  Wondering if anyone can explain that to me....

Mike

Chachere's picture
Chachere
Offline
Joined: 10/27/10
Posts: 674

Hard to tell without a diagram what was wrong.    But, for simplicity's sake, lets assume you had just one pair of 6V batteries in series (to get 12V).   If you take power from the positive terminal that's in the middle of that pair, you will get 6V.    Take your voltmeter and test each battery alone, you'll get something like 6.4V.   But if you test the pair by putting the probe on the positive at the beginning of the series and the other prove at the negative of the battery at the end of the series, Voila! -- 12.8V.    Same thing with your charging from the solar -- it needs to be at the opposite ends of the pair that are in series.    Think of the 2 6V batteries in series as just 1 12V battery.     
Nigel Calder's book "Boatowner's Mechanical and Electrical Manual" (which, if you don't have it, I strongly recommend having on board!) explains this far better.     Calder also recommends that if you are parallelling batteries, the positive and negative connections to the boat's DC system  should be opposite (or, said another way, "diagonal") from each other relative to the battery bank.  ( I tried to attached scanned images of diagrams, but for some reason the site isn't letting me upload them.)
 

McFly
Offline
Joined: 10/22/18
Posts: 190

This is great stuff.  I have sent you a PM.  I will get my diagram worked out and send you a copy.  As always, thanks!  

Mike

Log in or register to post comments