Battery advice?

[Mariner]

When we bought our boat (used) it had three main battery banks. There are the two 8D deep cycle batteries installed at the factory, one for starting, and one for house. They both charge of the same two bank charger, and off the engine's alternator. The previous owner (upon delivery) had a bank of four golf cart batteries installed as well to run the inverter. I created a link to be able to draw on that bank for house loads as well. It currently chargers only off the inverter/charger.

So, to review, there are three battery banks on the boat; start, house, and "golf".

When we bought the boat, we had a starting issue and were advised to replace the start battery, which we did. We did not replace the house battery. Now it appears that the house battery is dead. It does not hold a charge and even draws current off the start battery when combined.

The time has come to replaced it, but we want to be sure we do so with the best possible option. My first thought is that the 8D deep cycle battery we are currently using as a start battery would make a better house bank, and we might be smarter to move that one over, and replace it with a battery more appropriately suited for starting duty.

So, would it be posible to use a smaller, lead-acid battery for starting? I was thinking a high-end group 27 battery ought to produce the roughly 1000CCA's that the 8D deep cycle does, while taking up less space and weight. Do I need to worry about voltage differences when charging from the alternator? I have seen charging regulators that will protect a battery from over-charging, but are there any that are specifically designed for multi-bank setups? If so, what is the best? Ideally, I would like to have something that can intelligently charge all three banks, either equally, sequentially based on priority, or whatever I decide. Does such a thing exist?

Or, would we be better off to keep the 8D deep cycle as the starting battery and replace the house battery with something more suited for house loads like another set of golf cart batteries, or an AGM or gel battery?

[jcollins]

Mariner,
A timely subject for me as I had battery issues this past weekend. My setup is not as elaborate as yours. I seem to remember a thread from a few months past that I'm going to search out.

Rather than hijack your thread, I'll start another for my issues.

[Pitou]

On the little 28 my situation and needs are different, I run a 4D dual purpose starting / deep cycle for my starting battery (installed at factory) and I replaced the House Group 27 with a 4D combination starting / deep cycle made by Rolls Battery. The Rolls battery is a bank of six batteries tied together and if one bank fails it can easily be replaced. From what I understand you should not mix battery types. Stay with all lead/acid or all AGM's or all GEL's.

http://www.rollsbattery.com/

[Tuxedo]

A couple of thoughts.

You cannot mix gel and regular batteries. They charge at different rates and require different settings on the charger and alternator.

I have 3 4D batteries on Tuxedo. One 4D will not start my C-series Cummins; it takes at least 2. I set all 3 battery switches to ALL to start and run.

Note – facts end here and speculation begins.

I hadn’t thought about it, but I guess with the batteries interconnected, the voltage in all 3 equalizes and the alternator charges all 3 equally. It seems to me that alternator just charges whatever batteries are connected to it, so if I only used 2 to start and run the engine, only those 2 would be charged.

Therefore, it seems if you want the alternator to charge all 3 of your banks, all 3 would have to be available to start the engine. However, charging all 6 of your batteries might really stress the alternator.

Finally, I’d be very surprised if one group 27 would start your Cat.

Bottom line, keep what you got, buy an 8D at Sam’s or the auto parts store. With the weight of the batteries on board, one more won’t matter.

[AlMar]

I have one 4D for house use, and two 27's. I keep one for starting, and keep one isolated for the winch/bow thruster as I would raely use both at the same time. I run a 350 hp cat and only recently upgraded from a 24 to the 27. I only start with one battery, and did, in fact, use the 24 to start before the recent upgrade. I never gave it any thought, but I think I'd be concerned if I needed two batteries to start. Doesn't that leave you at a disadvantage if your "out there", and have to switch to TWO other batteries?
AlMar

[Mariner]

Well, apparently a set of two new 8D deep cycles were purchased for the boat, and delivered today, so that solves the problem for now, but we're still looking at long term solutions.

A couple things to clarify. It is my understanding that, if you use a computerized charge controller, it is ok to use different battery types, so long as they are not interconnected. Our battery charger already charges the two main banks independently, and the golf bank has it's own seperate charger. If we went with a differenty type of battery for the start or house bank, we would use a multi-bank charge regulator to ensure they charged independently off the alternator.

As of right now, we have no problem starting off the start battery alone. but it is a deep cycle that my research indicates should be capable of about 1000CCAs and a lot of amp-hours. But we don't need amp-hours, we just need a lot of CCA's to turn the motor over. I was looking and many of the heavy duty and extra heavy duty group 24 and 27 lead-acid batteries put out the same CCA's but much less amp-hours. I was thinking this may be a viable option, so long as we dealt with the difference in voltage when charging off the alternator.