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KindOfBlue 02-11-2009 04:12 AM

Battery Re-design question
I currently have 2 decent sized house banks that are also used to start up the engine.

Each house bank consists of 4 6v Trojan T105s (total of 8).

I really don't like the design because when one bank drops down to about 50%, I hesitate to use much of the 2nd bank because if I drain that too low, I won't be able to start the engine.

I recently bought an Xantrex Echo-Charge and my plan is to pull off 2 of the Trojans to make a starting bank and then use the remaining 6 for my house bank.

As far as I know, these Trojan T105s are deep cycle and I am wondering whether or not I should be using "Starting Batteries" for my starting battery. It may actually be easier for me to buy and install a new 12v starting battery.

If I can and should get a new starting battery, can I get a AGM or do I have to stick with wet?

xort 02-11-2009 06:59 AM

what engine are you starting?

I have a perkins 4.154 62hp engine. I use a standard group 31 starting battery with 1000 CCA.
I would combine all the 6v batteries into one large bank and add a starting battery.
all chargers that I know of want to only charge one kind of battery, so don't mix in AGM with your wet cells

Buy calder's boat owners mechanical and electrical manual. Detailed explainations on what, how and why for all this stuff. Or one of Don Casey's electrical books

ehmanta 02-11-2009 07:21 AM

I'm with XORT on this, pair down your starting bank with a single battery and increase your house bank to 6- 6 volt T105's. You may want to wait until your current batteries are finished because re-arranging them now will shorten there lives a bit. Some here will tell you that one big bank works fine, but I would only do this IF you have a pull start generator ready to go.
The banks you have right now is mighty big (and heavy) for a 38 foot boat......unless of course you have the hot tub option with the 1000w stereo!!!:)
Happy Sails

KindOfBlue 02-11-2009 07:34 AM

I have Calder's book, but with the Echo-charge, you don't actually connect your typical charger to the starting battery. The echo-charge connects the house to the starting battery and will sense a charge on the house (from your charger, alternator, solar, etc.) and then float some of that charge over to your starting battery to top it off.

The instruction manual on the echo-charge says this:

"Only similar batteries should be connected together in one bank. Do not
connect old and new batteries together or wet and gel cell batteries

I think that this is referring to a bank and not the entire system. If so, I can use an AGM dual purpose for the starting battery. Anyone?

My engine is the Yanmar 4JHE (about 45hp). The manual doesn't spec out CCA or MCA, but does say that you want between 100 and 150 AH. I think for starting, I need to be concerned about Cranking Amps. There is a Group 24 dual purpose AGM at WM with 735 MCA. Anyone know if i can use this as a starting battery for this engine? (This is assuming that I can use an AGM with the echo-charge).

billyruffn 02-11-2009 09:01 AM

I have two house banks, one of which is 6 T105s. There's also a separate, single 12V starting battery (also Trojan). I've have had no problems despite the "mixing" of battery types -- the batteries are six years old and seem to be holding up well.

JohnRPollard 02-11-2009 09:23 AM


Originally Posted by KindOfBlue (Post 446461)
...I think that this is referring to a bank and not the entire system. If so, I can use an AGM dual purpose for the starting battery. Anyone?

Well, we were discussing this the other day and Camaraderie reminded me that the optimum charging voltage for wet cells is actually a slight bit higher than for AGMs. But that was with a "smart" battery charger.

Are you talking about charging from a battery charger, or simply off an alternator, or both? Does the alternator have a "smart" regulator that is adjustable for battery types, or is it a simple stock alternator with a pre-set internal regulator? Do you know what voltage that regulator is set for?

Answers to those questions would be helpful. But my gut is that an AGM starting battery should be okay if it's getting the juice from an echo-charger. But there are some sealed lead-acid starting batteries that might work just as well.

btrayfors 02-11-2009 09:35 AM

I'd combine all the T-105's into a single house bank, and connect ALL onboard charging sources to charge that bank.

Then, add a Group 31 starting battery -- flooded or AGM -- and an EchoCharge device to maintain that starting battery.

Unlike deep-cycle batteries, starting batteries are designed with thin plates to deliver a lot of amps quickly, for a relatively short time. This will make your engine very happy. And the EchoCharge will make the starting battery very happy.


camaraderie 02-11-2009 11:42 AM

Kinda...I think your instincts on this are fine and Trayfors as usual provides the correct but boring solution! C'mon Bill...we need a NEW solution...change and hope ya know!! :D :D :D

KindOfBlue 02-11-2009 11:46 AM

I am charging the house bank off of Charger, Alternator and Wind Generator. I know that the Charger and Alternator have 3 stage charging. The wind generator has a regulator, but I think that it just a simple one.

The charger and alternator have been tuned for the specifically for the Trojan lead acid batteries that I have. The only source of charge on the echo-charger will be a spill over from the house bank.

btrayfors 02-11-2009 12:39 PM


That's fine.

Cam was just pulling your chain a bit, and mine :-)

Boring, yes, but the way to go for sure!

Let us know how you like it after a few months.


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