Why more than 1 battery?

CC38EL · 10-27-2008, 07:25 AM

I am seriously looking at replacing my 3 12v deep cycle coach batteries with 1 large 12v deep cycle battery. I'm growing tired of the maintenance and all the cables between me and the end battery.

Weight would be less and amps about the same. Currently, I'm running 3 marine/RV deep cycle with 115amp rating each for a total 345amps at 67lbs each for a total 201lbs. A good 8D that I'm looking at puts up 480amp rating at 186lbs.

As always, if you have comments, feel free to contribute. I know the risk of a single battery, but we don't boon dock that much and with dual engine starting batteries, I can always jump in reverse.

Anyone out there running just 1?

Regards,

CC38EL · 10-27-2008, 07:25 AM

I am seriously looking at replacing my 3 12v deep cycle coach batteries with 1 large 12v deep cycle battery. I'm growing tired of the maintenance and all the cables between me and the end battery.

Weight would be less and amps about the same. Currently, I'm running 3 marine/RV deep cycle with 115amp rating each for a total 345amps at 67lbs each for a total 201lbs. A good 8D that I'm looking at puts up 480amp rating at 186lbs.

As always, if you have comments, feel free to contribute. I know the risk of a single battery, but we don't boon dock that much and with dual engine starting batteries, I can always jump in reverse.

Anyone out there running just 1?

Regards,

smlranger · 10-27-2008, 08:49 AM

I'm certainly no battery expert, but according to your stated specs, looks like you would be fine. However, how in the world do you get a 186 lb battery in that tray?

CC38EL · 10-27-2008, 09:29 AM

Oh...that's easy. Me, a six pack and a special stainless steel athletic supporter.

Actually, I'm hoping the place where I get this battery has a dolly or small lift. Like the one used by the airconditioning folks to take the basement a/c unit in and out.

SCVJeff · 10-27-2008, 11:07 AM

BTW- Dunno if you have the same tray, but I talked to Winne and Kwikee a year ago about the ratings of my tray (they actually never had anyone inquire..). After almost 2 weeks of searching they found the original stamped drawings for the tray and square stock cage of the Meridian/ Journey, and it's rated at 250lb.

Jeeperrmartin · 10-28-2008, 05:34 AM

ua40j

If you do that be sure to post the results, as I have also thought of that combo.

John_Canfield · 10-28-2008, 08:00 AM

One 8D battery is a *great* idea in my opinion if you can deal with the weight. Having multiple batteries in parallel is generally not a good idea because a problem in just one cell of one battery will affect the entire bank.

On the boat we had an 8D, a 4D and a couple of deep-cycle group 27s for starting the diesel.

I recommend a marine gel 8D - check out West Marine for price comparisons.

BryanL · 10-28-2008, 12:50 PM

the bad cell problem is not restricted to banks composed of parallel batteries!

If you have one battery that gets a bad cell you are SOL. If you have batteries in series and one gets a bad cell, you will also have an unusable bank.

Fortunately, bad cells are less common than they used to be. With a parallel configured bank, you can pull a bad battery. This redundancy can be an advantage.

Jim · 10-29-2008, 04:11 AM

hi..one original group 24 battery went out after 4 years..i don't boondock much so i unhooked it and ran on the other battery for 2 more years..bought 1 new battery and have been on it for another 2 years without problem..i have to put water in the battery every 2-3 months..same as when i had 2 batteries..if the battery goes bad i am only a few miles from a walmart,sears,etc. so i don't worry about it..jim..

jimandsue60 · 10-29-2008, 05:05 AM

I think you might be looking at the wrong ratings. I went to the Trojan Battery site and compared their 8D with group 31 12 volt marine batteries. The 8D will give you 230 amp at the 20 amp hour rating where 3 group 31s will give you 330 amps at the 20 amp hour rating. If you were to replace with 4 6volts batteries you would have 440 amps at the 20 amp hour rating.

If your ultimate goal is to keep it simple the 8D is the way to go. Keeping in mind you will be loosing battery capacity.

dirko · 10-29-2008, 06:43 AM

Hi Ho: Now I'm confused. House batteries are rated in amp-hours, not amps. We're really not interested in the surge current rating as with starting batteries.

I just assumed that y'all had just shortened amp-hours to amps, except that JimandSue60 have apparently reversed the terms. How many amp-hours one gets is a function on the discharge rate, so be sure that your expectations are tempered by the discharge rate as well as the point (battery voltage) at which the battery is considered to be discharged.

By the way, batteries last a lot longer if they are not deeply discharged.

Dirk

tderonne · 10-29-2008, 07:33 AM

Yup, things are getting a bit messy.

I'll add one more thing. When you pair to 6 volt batterires to make one 12 volt, you don't add the amp-hours. You do add the reserve capacity (in minutes) though.

And there are different discharge loads used to measure it all, 75 amp, 25 amp. Really gotta dig deep and be sure you're comparing apples to apples.

jimandsue60 · 10-29-2008, 08:26 AM

My main point was that the OP was not comparing apples to apples.

"I'll add one more thing. When you pair to 6 volt batterires to make one 12 volt, you don't add the amp-hours. You do add the reserve capacity (in minutes) though."

You do add the amp hours if you have 2 sets of six volt batteries tied together.

Jim

MrTransistor · 10-29-2008, 10:14 AM

Hi Tim,

Actually, the Reserve capacity is very much like Amp./Hours. It comes from an automotive requirement that sets a discharge current (25 Amps.) that is comparable to leaving on all the lights on an average car. That way you can approximate how long till total failure you have at night if the alternator were to fail.

Net effect is that Reserve capacities like Amp./Hour ratings do not add when two 6 Volt batteries are connected in series, it is the same as for one 6 Volt battery.

Amp./Hour capacities do not add when two 6 Volt batteries are connected in series, it is the same as for one battery.

Voltage for two 6 Volt batteries connected in series does add and is 12 Volts.

Any time batteries are connected in parallel, the Amp./Hour capacity and Reserve capacity are added.

Examples: Assume all batteries are 6 Volt 100 Amp./Hour

1ea. = 6 Volts 100 Amp./Hour
2ea. in series = 12 Volts 100 Amp./Hour
2ea. in parallel = 6 Volts 200 Amp./Hour
3 ea. in series = 18 Volts 100 Amp./Hour
3 ea. in series-parallel = not allowed (or until the fire starts)
3 ea. in parallel = 6 Volts 300 Amp./Hour
4 ea. in series = 24 Volts 100 Amp./Hour
4 ea. in parallel = 6 Volts 400 Amp./Hour
4 ea. in series-parallel = 12 Volts 200 Amp./Hour

This same math applies to any battery or cell as in 1.5 Volt flashlight batteries. Three in series = 4.5 Volts at the same Amp./Hour capacity as a single cell. A rectangular 6 Volt lantern battery (the kind with two springs on top) is made up of 4ea. 1.5 Volt cells internally connected in series.

My research a while back showed that 4ea. 6 Volt batteries could occupy the space in the slide out tray most efficiently. As such, more weight could be installed and weight equals lead and acid solution which equals higher Amp./Hour capacity compared to an 8D truck battery. By the same token, AGM's by design have more space internally for the lead plates and need less volume of acid solution and weigh, on average, more per cubic inch than flooded deep cycle RV/Marine batteries do.

I didn't look into price comparisons between 6 Volt Group 31 and 12 Volt Group 8D RV/Marine but I suspect that you would pay a premium for the 8D just because of production volumes. It boils down to capacity vs. convenience. If you don't need the capacity, then the 8D would be convenient by eliminating four jumper connections. If capacity is the requirement, I think that 4ea. 6 Volt Group 31's would

tderonne · 10-29-2008, 10:35 AM

There was something that still adds up with 6 volts. No matter. I think Mark explained it all.

I did some of the math when I went to 4 6 volt batteries. Much like Mark, I figured that used the space available the best. And Sam's Club "Energizer" batteries are WAY cheaper than anything on the market for what you get. (They are sold BELOW cost according to a friend in the battery part of Johnson Controls.) Working great so far....

CC38EL · 10-29-2008, 04:12 PM

I thought I should put in 115 minutes capacity at 25amp load per battery for the 3 batteries. And again 460 minutes capacity at 25amp load for the single battery, but I got lazy and just put amp rating. You can use whatever values you want to, as long as you compare apples to apples as someone noted.

My bad. Sorry for the mess. Here's a piece of information that I found interesting:

http://www.smartgauge.co.uk/batt_con.html

Changing the connections on my battery setup intrigues me. I've never thought I got the most out of the battery setup I had. It always seemed less than the numbers indicated. Perhaps just changing the way the voltages/amps are pulled off and put back on is the best way to keep redundancy and capacity at the same time.