I would like to replace the single 12 volt coach battery with two 6 volt Trojan T-105's or two 6 volt Interstate U-2200's. A few months ago I replaced/upgraded the Power Converter to a Parallax 7345RU, 45 amp unit. The question is, will there be any problems with the charging of the two 6 volt units by the 7345,, will it be ok w/the 4k Onan Generator, the shore line or the Alternator on the engine? I've read pages & pages of information here on the site but I'm just more confused then when I started. I'm very mechanically inclined but I'm totally confused by the battery 'technology'. I'd really appreciate any and all help.
'93 Ford E-350/29' Class C w/7.5 eng.
Thanks for any help......
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Apologies to 'Lobo'
It is all about the amp hours. I would buy the 6 volt battery that delivers the highest amount of amp hours. For example, If you buy 2 6 volt batteries with 220 amp hours each, you connect them in a series which doubles your voltage to 12 volts. Your amp hours remains 220. If you buy 2 12 volt batteries with 115 amp hours each, you connect them in parallel, which keeps the voltage at 12 and doubles your amp hours to 230. Your converter and generator will be just fine with this setup. Good luck.
The Parallax 7345RU will put out one voltage ~13.6 volts (VDC) at up to 45 amps (less whatever other loads are drawing) to the batteries. That will:
Charge your new batteries, albeit slower than a three-stage charger that will start out at ~14.4 VDC.
Cause you to lose water from the batteries, so you will have to keep an eye on the electrolyte level at least once a month, more frequently in the summer. A three-stage charger would float the fully charged batteries at ~13.2 VDC, greatly reducing the water loss.
Other than that, it will work fine.
Our Minnie came standard with a Parallax 7245 and had an option of two 6-volt batteries.
The simpleesttttt thing to do is measure your battery compartment, then buy the 2 biggest 12 volt batterys you can find, the more plates the better, the more amp hours the better, a new pair of the exact same batterys the better.
It is very easy to get confused by all the technical info. that pours in from every where. I bet you I have posted the basic battery formula on this site at least 40 times, and people still argue about it.
Your generator don't care, it just puts out what it can, if you ask it for to much it runs out of fuel and are burns up.
Two six volt batteries in series make one 12 volt battery, as far as your generator, shore line, converter / charger, or alternator are concerned. The only difference is that you now have 225 amp-hours at 12 volts, of rated capacity, in the case of the Trojan T-105's. Your present single 12 volt battery probably rates no more than 105 amp-hours. Of course this means that if you draw the new batteries down to 50% discharge, it will take longer to recharge them than the same 50% does now.
Yes, the Parallax isn't as fast on intitial charging as the best three-stage type, and doesn't cut back into a float mode as those do, but it will do your job. Just check the fluid level in the batteries often and add water when needed.
I trust you've confirmed that you have room for the twin 6 volt batteries. If so, go for it.
Thanks folks. Nice and easy to understand answers! Casey, The actual battery cavity is just (barely) large enough to hold 1 battery but the cavity next to it is huge. I will 'vent' the new site though. Interestingly, the existing battery cavity is NOT vented!? Go figure.
Thanks again for not putting me into 'technical overload' with too much (unnecessary) information.
The common problem in using the popular Trojan golf cart batteries is height -- they're tall for their size. By the way, there's nothing wrong with mexfishguide's recommendation for 2 x 12 volt batteries, except -- it has been pointed out that the golf cart types are rated at much longer life, measured in number of discharge/recharge cycles. They at least claim to be better built for deep discharge use. But for that consideration, and size, you can basically buy deep cycle batteries by the pound -- more weight, more amp-hours. Just be sure you can still lift the darn thing!
It's probably less important that a battery compartment be vented than that there's nothing in there that can make a spark. This includes wiring arranged so it can't vibrate loose and touch something it shouldn't. Still, ventilation is a very good idea. The explosive gas is hydrogen, which is lighter than air, so vents should be at the upper side of the compartment, and ideally at upper and lower sides, so some air circulation can occur.
If you are thinking the 7345 will quickly charge those batteries, I strongly recommend you read this topic and look at the links provided in it: Generator/Battery Question.
Adding to Caseydon's statement, battery compartments must be sealed from the interior and must have vents at the top and bottom per the National Electric Code.
Casey & Mel: Boy, did you guys throw a monkey wrench into my pond! I went out & checked again and the actual battery compartment (MFG labeled!) is just large enough to fit 1 standard type of 12 volt car battery and doesn't have any vents! It does have a key lock, a warning label on the door and the connection wires for the terminals. I pulled the battery just to be very sure about the vents. The storage bay next to the battery bay has plenty of room HxWxL for anything, and I can build a battery-container w/vents to keep everything safe. That's the easy part... Mel, I read and re-read the link you gave and went to the links within that link.... and I'm fully confused again. I replaced my faulty 6300 converter with a 7345RU just a few months ago -- but the way I read the information it won't work well with the extra AH's. So what do I do? I need to replace the existing battery (it's shot) anyway - do I go the (2)6 volt, (2)12 volt or do I find a single 12 volt unit again? If I jump to the (2) batteries do I toss the new 7345 out the window, do I use an external charger? Aghhhhhhh. I do know if I keep the same battery location I will drill some vents pretty quick!
We did some winter boondocking and I found that the (1)12 volt battery would not last long enough to keep the heating system working through the night - so, I guess the question is, what would YOU do?
And thanks guys, I truly appreciate your spending valuable time to help me out with this.
Oh, Casey -- Thanks for the warning about the heavy batteries, I'll leave the lifting to the DW Uh, honest honey, I didn't write that......
Floyd -- Sorry to re-complicate your project, just when you thought we were helping to simplify it. Let's see if we can get back on the road to a simple reliable solution. My own set of experiences may help.
I had one of the Magnetek converters which was essentially single stage -- slow to recharge and unwilling to cut back so as not to cook a charged battery. I replaced it with a WFCO conversion kit, supposed to be 3 stage -- full amp bulk charge, constant voltage absorption, 13.2 volt float. Well, for practical purposes, that first stage ain't there! Even a new battery, 50% discharged, causes it to cut back to a few amps within a few minutes -- bah! The only good news is that it does hold a charged battery at 13.3 volts with no water loss in over a month. My solution to this problem has been to buy a 20 amp Xantrex Truecharge 4 stage battery charger (not a converter/charger). I'm wiring it for plug-in, semi-portable operation, and plan to throw the breaker on the WFCO when I use the Xantrex. That's so it will see the battery's voltage and not be confused by the WFCO's "contribution". These 4 stage chargers aren't cheap, but I'm expecting this one to work. I bought a 20 amp size since I only have room for one battery, a Trojan SC225, 130 amp-hours at 12 volts.
As for what new battery(s) you should buy, it seems you know that one battery isn't enough for your needs. Of course any good new one would have more capacity than your worn-out one. Beyond that, you're back to amp-hours, of which, like money, everybody wants more. My thought is that if your present compartment only holds a Group 24, rated at 85 amp-hours, or even a Group 27, at 115 amp-hours, you should go on to build a new compartment to house two batteries. Whether they should be 2 x 6 volt or 2 x 12, take your choice. Two T-105's gives you 225 amp-hours, two T-125's give 240 amp-hours (at 66 lb each, DW), and two SCS225's give 260 amp-hours, also at 66 lb each. I hope DW is a strong lady.
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I went out & checked again and the actual battery compartment (MFG labeled!) is just large enough to fit 1 standard type of 12 volt car battery and doesn't have any vents! It does have a key lock, a warning label on the door and the connection wires for the terminals. I pulled the battery just to be very sure about the vents. The storage bay next to the battery bay has plenty of room HxWxL for anything, and I can build a battery-container w/vents to keep everything safe. That's the easy part... Mel, I read and re-read the link you gave and went to the links within that link.... and I'm fully confused again. I replaced my faulty 6300 converter with a 7345RU just a few months ago -- but the way I read the information it won't work well with the extra AH's. So what do I do? I need to replace the existing battery (it's shot) anyway - do I go the (2)6 volt, (2)12 volt or do I find a single 12 volt unit again? If I jump to the (2) batteries do I toss the new 7345 out the window, do I use an external charger? Aghhhhhhh. I do know if I keep the same battery location I will drill some vents pretty quick! 
