Final decision made today on batteries

[Scott & Heather]

I have read a lot of posts about batteries here, thank you so much to all of you who have posted over the years. I am learning. I have found that it is very difficult to find 8DAGM batteries locally, and they are very expensive to ship. Would I be wise to use 4 group 31 batteries as my start/house battery bank? It won't be the end of my battery bank it is just the beginning. And for now they will only be used as start batteries until I actually get an inverter. I have read the arguments against using deep cycle batteries a start batteries, but I am confident that there is enough cold cranking apps for this to work. Plus I will be adding more batteries to the max very soon. I also know that it's not conventional to use your start batteries as house batteries in a combined battery bank, but once again I am taking a slightly different road as I have done many times with this bus and it has worked for me. Well I want to know is if for group 31's will do the trick? I have read several times were people used three group 31's? I'm not 100% sure why they would use that configuration?


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[richard5933]

I'd be one of those who would urge you to separate the start & house batteries.

If you have room for 4 batteries, couldn't you use two for house and two for start? For so many reasons your proposal seems fraught with potential for problems, and the main one I'd always fear is being left with batteries too weak to turn the engine and start. All it would take is accidentally walking away or falling asleep with power on to something and coming back to a bad situation.

Richard

[luvrbus]

3 group 31's are for a 12 v system wired in parallel  for a 24v system you use 2 or 4 (12v) batteries wired in series  

[Jon]

What Richard said. Owning a bus and doing it right means you have to spend a dollar or two.

[bevans6]

I would be more inclined to use start batteries as a combined temporary house/start bank.  Without that big inverter the deep cycle loads on the batteries will be very small, and start batteries can handle that just fine.  Start batteries are optimized for quick delivery and acceptance of power during and after starting, will handle the small house loads fine, and you can add deep cycle batteries when and if you decide to.

Brian

[Scott & Heather]

Thanks cliff. That's what I needed to know. Guys, there are several on various bus forums who have successfully built only one combined bank for starting and for house. I'm headed that direction and in that camp. Definitely appreciate the heads up for the issue this could cause and I might be back on here eating crow soon (and I will own up to it if this is a huge mistake) but I've done a few things really unconventional on my two bus conversions including a combined black grey combo tank with grey diverter valves  as well as things like putting drywall in my bus and other things many said shouldn't be done, and yet it works for us perfectly. I have twin Honda generators that can charge my batteries if they get low for a start situation and I will eventually have such a large bank that even at a 50% discharge they should start the coach no problem. Again, reading through the history on here there's a good few who have done this...bob of the north I think is one of them. Also, 4 group 31 deep cycle batteries even with the slightly reduced CCA will still start my coach. Remember, for two years I've been starting my coach with TWO group 31's even in the dead of Michigan winter (no block heater installed yet) so I should be ok in that area. Thanks again for the advice, I always appreciate it. I'll report back how I like or hate this setup. That being said, I am installing a dual group 31 batter setup in my toad that can and will be used to start the bus in a majorly messed up situation if ever needed.


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[TomC]

I have talked directly to Lifeline AGM battery factory. They said that the power and output of the batteries are directly in relation to how much they weigh. Two 8D's will give 510amp/hr. 5-31 batteries will give about the same. Plus size 31 batteries are a whole lot easier to handle then the 8D's.  Good Luck, TomC

[windtrader]

Scott,

If you placed your order, i'm too late. Having just spent many days deep diving into battery technology, I'm hoping to have made solid design and purchase decisions for my RV requirements.

Start, marine, and deep cycle are designed differenty, each optimized for the type of use. Start batteries provide high amps for short durations, deep cycle batteries draw less amps for longer durations, and marine batteries are hybrid to serve as both start and deep cycle.

The plates in start batteries are thinner while deep cycle are thicker. You can actually see the difference if you look into the holes.

SOC (State of Charge) and DOD (Depth of Discharge) indicate how much power is in the battery. 100 pct SOC and 0 pct DOD indicate battery is full.

Starts are designed to remainn above 80 pct SOC, so you really have only 20 pct usable power from the battery. Deep cycle can go to 50 pct DOD with little damage, Both types suffer from reduced cycles the more you draw them down. Refer to charts showing this characteristic.

The main advantage of starts is you get more power with less battery; this works perfectly for starting motors in the most cost effective manner.

There is no technical reason that I can discern that a deep cycle bank offering the same cranking amps as the start should work fine. Naturally, most do not choose this path due to increased cost, weight, and maintenance.

Using start batteries for deep cycle purposes is a bad idea, plain and simple. If you plan on using the battery bank for house use then choose deep cycle. Deep cycle can start, starts as house will unperform.

On the topic of single bank vs seperate. The most important and critical functtion in your coach is the abbility to start. Unless you can guarantee your single bank will never get drawn down to the point of starting your coach then you are ok. If not, then seperate banks are needed.

Two banks tied together is how I'm currently configured with two disconnects. Between the house and start there is a disconnect sepearting them so the start will always keep a charge. Between the coach and the start is a disconnect to protect the start from any draw from the coach, again protecting the start.

When underway I connect the house and start if I want the alternator to charge both banks. Under certain circumstances I'll let both banks serve house needs. If ever the start gets run down, my generator can charge up both banks so the bus will start after a bit of charging.

Without a house bank disconnect, it is possible to draw the batterry down to zero, a fatal condition. I'm planning to add a disconnect in the house bank to prevent such a total draw down when unattended. This did happen to me as the refrigerator uses some DC while running on propane, so it is a real world event.

Don 

[Scott & Heather]

Any advice at this point is too late. 4 brand new group 31 AGM's are sitting in the back of the land cruiser waiting for me to install tomorrow


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[bobofthenorth]

I have talked directly to Lifeline AGM battery factory. They said that the power and output of the batteries are directly in relation to how much they weigh. Two 8D's will give 510amp/hr. 5-31 batteries will give about the same. Plus size 31 batteries are a whole lot easier to handle then the 8D's.  Good Luck, TomC

I don't know how the new lithium technology works but with any battery based on lead plates this is absolutely true.  Weight equals capacity.  More weight is better. 

[Scott & Heather]

These suckers are crazy heavy. Stupidly so. And I'm young and buff. Ok last question, can someone draw me a diagram on the best way to set and wire these? I know three fit width wise across the battery bay of my MCI and one has to go long ways in the back behind those three. Something like this, but i keep drawing wiring diagrams and my head is spinning. I have to do this right. Can someone help? 24 volt bus. 4 group 31 12 volt batts. I left out the polarity of the other batts because I honestly don't know how to sit them?? I know two in parallel and then the two sets get wired to each side of the bus negative/ground and positive:


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[Scott & Heather]

This is the best configuration I could come up with...right? Wrong?


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[bobofthenorth]

That makes sense to me Scott.  You'll also have to connect the middle negative to the top positive but you already knew that.

The goal is to keep the total cable length on the negative and positive paths as equal as possible.  I'm not convinced it makes much difference on that short of cables but some know it all will question it if they are obviously different. 

[eagle19952]

[eagle19952]