Adding batteries

[tykesplace]

Hi all,

I have a pull trailer. There are two batteries mounted to the hitch frame between the front of the trailer and the propane tanks. I'd like to add two more batteries to extend dry camping time. I can't find any secondary rack kits or anything to do that. Maybe I have to build one. Does adding batteries seem like a reasonable thing to do to increase capacity? The local RV store says I should go to two higher capacity golf cart batteries saying that would give me about a 50% increase in capacity.

Thanks!

 

[John From Detroit]

Try this... What size are those batteries?    Here is why I ask.

A Group 24 battery holds about 75 amp hours, 2 of them 150 but you can only use about 50 of those safely (Actually a bit less) before battery damage starts becoming serious. if they are the common "Marine Deep Cycle

Group 27 and 29 either side of 100 amp hours each but again you can only use about a quarter of it give or take a bit safely.

GC-2, which is taller, heavier but not much different footprint from a G-24 holds 230 amp hours per pair and you can use 115 of them safely before damage sets in.

Same number of batteries,,, Bit taller, but 2x the usable power.

GC-2 are DEEP CYCLE, and the rule is keep them at least half full..

What happens if you "OPPS" and run 'em way down?

Well, I've only worked with one pair of GC2's personally in recent years.. Used to use that size alot but those were starting batteries,,, These are DEEP CYCLE Interstate U-2200's.  I've taken them down to the point where my steps would not extend, my lights would nto light, I could not crank the generator (had to use an isolated battery to start it) more times than I care to admit (At least 5) and they still test well.

Nearly every time I've taken a startin battery down like that... I had to replace it.

 

[Jammer]

I have a pull trailer. There are two batteries mounted to the hitch frame between the front of the trailer and the propane tanks. I'd like to add two more batteries to extend dry camping time. I can't find any secondary rack kits or anything to do that.

http://www.rvplus.com/modular-plastics-div-battery-box-vented-kit-includes-9-250-276kit.html?utm_source=googlepla&utm_medium=cse&utm_content=AR-210471&utm_campaign=googlepla&gclid=CLbXifHujrYCFVKf4AodtXMArg

http://www.bestconverter.com/Battery-Boxes_c_118.html

Maybe I have to build one. Does adding batteries seem like a reasonable thing to do to increase capacity?

Yes.  Depending on your situation you might also be able to add one under the hood of your truck, which I have done, which will help particularly if you leave your trailer in one place and drive your truck while hunting, sightseeing, etc.

The local RV store says I should go to two higher capacity golf cart batteries saying that would give me about a 50% increase in capacity.

That's pure, unadulterated bunkum, unless the batteries you already have in your trailer are either a) crap, or b) smaller than what you have room for.

Most RVs have room for a group 27 battery.  Batteries are installed by the dealer, not the factory, and so if your dealer installed a smaller group 24 battery, or maybe a cheap dual-purpose battery that isn't really a deep cycle battery, then you'll get poor performance.  Batteries only last a few years so if yours are older maybe they just need to be replaced.  Just get a couple of good deep-cycle group 27  batteries from the discount store and put them in and you can leave the wiring alone and avoid paying $$$$ to the stealership.

If you compare the output ratings on GC-2 and group 27 batteries, you'll find that the capacity is nearly identical. 

 

[Jammer]

A Group 24 battery holds about 75 amp hours, 2 of them 150 but you can only use about 50 of those safely (Actually a bit less) before battery damage starts becoming serious. if they are the common "Marine Deep Cycle

Group 27 and 29 either side of 100 amp hours each but again you can only use about a quarter of it give or take a bit safely.

GC-2, which is taller, heavier but not much different footprint from a G-24 holds 230 amp hours per pair and you can use 115 of them safely before damage sets in.

Same number of batteries,,, Bit taller, but 2x the usable power.

Pure bunkum on the 2x usable power, there, John, sorry.

A pair of true deep cycle group 27 will last just as long at 50% depth of discharge as a pair of GC-2s.  Sure, if you want them, you have room for them, and you want to change the wiring around, great; there are IMO some benefits involving reliability but they are minor.

But don't lead the noob down the primrose path.  Modern deep cycle group 27s from the local discount or big box place are readily available and you can run them down to 80% dod and as long as they are recharged promptly and otherwise cared for they will last 4-5 years.

 

[John From Detroit]

I almost agree with you.. A pair of G-27 Deep cycle, if you can find 'em will be about 200 amp hours compared to 230 for the  GC2 pair,, Close but not exact. (not enough difference to argue about)

The problem is that you are more likely to get Marine/Deep cycle, and those should not be taken to 50 percent.  They are primarily starting batteries.

But then I was specific on that point in my earlier post.

And yes, I do know you can get Group 27 Deep cycle, Just "If you can find 'em" I've looked with little sucess on most occasions (I have found them but alas, by the time I had money they were gone).

 

[Gary RV_Wizard]

Odds are he now has Group 24 marine batteries, which means he about has 2 x 80 AH = 160 AH. Changing over to 2 x Group 27 deep cycles will yield about 2 x 105 AH = 210 AH or a  30% increase.  Changing to 2 x GC2 golf cart deep cycles yields 230 AH, or about a 45% increase. Close enough to 50% for saleman-speak!

Any of these had a usable Ah capacity of about 50% of the max rating. A bit less on the marine batteries and maybe a bit more of the golf cart batteries, but right around 50%.

 

[Derby6]

I don't wanna make this thread go astray, but have you considered solar panel(s)?  Higher up front cost but I love mine.

 

[jmugs]

I was going to buy 2 new 12V deep cycles, but if I'm understanding this correctly I'm better off with 2 X 6V batteries.

Sorry, but numbers confuse me to no end.
(I've had to deal with this learning problem all my life and it really stinks.)

Thanks for dumbing it down to my level.

 

[tykesplace]

Wow. Thanks for all the quick replies. The existing batteries are Interstate Deep Cycle Marine/RV SRM-24 550 CCA, 690 MCA. Dated 2/11. Does that mean group 24? We've only bought this trailer last summer, so I'm still learning. I don't know how well the batteries were maintained before we bought it. While parked at home I always have the trailer plugged in.

We did a couple of dry camps last year. We were conservative with using lights and such, but by the end of day 4 I had to hook up the truck to get the slider back in. That's happened twice. I don't know if that is damaging to take them that low. But they don't stay there. I get them recharged right away. We'd like to go a week and still have lights. So I was just thinking I could add two batteries and double capacity. I would just build the metal rack to hold the weight and add a box and cables.

How about these? $99 from Sears? DieHard Marine Deep Cycle/RV Battery, Group Size 27M

Gary: I just found the GC2 at Interstate, but they're 6v. Would two of those wired in series for 12v be better than the two SRM24s?

Jammer: Why would I add a battery to the truck? Not that I can, just wondering why?

Derby: I have considered solar but we live in western Montana, and most of the places we've gone so far have been pretty wooded with no direct sun. Plus they're expensive.

 

[Jim Godward]

Tykesplace,

If you are mostly camping the forest and state parks, yes solar is not an effective way to go but if in campgrounds, you won't need it.  A good compromise would be the small Honda generator for charging the batteries.

The batteries you have are not true deep cycle and so will not do as well as real deep cycle ones like the GC2, etc.  I would try to sell or trade the ones you have and go for 4 GC2s which will do much better. 

If you do get the Honda generator, you can put off any battery change for a good while though.  Just a thought.

 

[Jammer]

Wow. Thanks for all the quick replies. The existing batteries are Interstate Deep Cycle Marine/RV SRM-24 550 CCA, 690 MCA. Dated 2/11. Does that mean group 24? We've only bought this trailer last summer, so I'm still learning. I don't know how well the batteries were maintained before we bought it. While parked at home I always have the trailer plugged in.

Yes, those are group 24.  You can measure the battery compartment to see if you have room for something larger.  You can also consider group 31 batteries if you have room, which would give you a little more capacity than group 27, although they are a little harder to find.

We did a couple of dry camps last year. We were conservative with using lights and such, but by the end of day 4 I had to hook up the truck to get the slider back in. That's happened twice. I don't know if that is damaging to take them that low. But they don't stay there. I get them recharged right away.

They'll be fine as long as they are recharged promptly.  It sounds like you have a working charge line on your truck, which will provide at least some charging, and if you plug in when you get home or to storage you'll be all set.

We'd like to go a week and still have lights. So I was just thinking I could add two batteries and double capacity. I would just build the metal rack to hold the weight and add a box and cables.

That works if you have room, but watch the tongue weight.  You're adding over 100 pounds right on the tongue.  If your hitch and tow vehicle can handle it, great, but if you're already on the edge that might be too much.

How about these? $99 from Sears? DieHard Marine Deep Cycle/RV Battery, Group Size 27M

Those are dual-purpose batteries.  Avoid them.  Look for a battery that has a rating in amp-hours.  Try Batteries Plus, Walmart, or Costco.  Some local/regional discount stores also have them -- around here Mills Fleet Farm and Menards both do.

Gary: I just found the GC2 at Interstate, but they're 6v. Would two of those wired in series for 12v be better than the two SRM24s?

They'll work great if you have room and are willing and able to change the wiring.  On my trailer I don't have room.

Jammer: Why would I add a battery to the truck? Not that I can, just wondering why?

Several reasons:
1) The battery has to go somewhere and if you put it in the truck you avoid running up the tongue weight and don't have to make a box for it.  You can buy a 2nd battery kit for most full size trucks from the dealer, and they're typically not expensive.

2) If you wire it up to the charge line with a battery isolator of some kind, it will be electrically equivalent to having the battery in the trailer as long as the trailer's plugged into the truck.

3) When you drive the truck, the battery charges from the alternator, so if you have a camping pattern where you park the trailer and drive the truck every day, the battery recharges a little.

4) If you do not have power at your storage location you will still be able to start out your camping trip with some 12v power available, assuming that you drive your truck regularly.

Derby: I have considered solar but we live in western Montana, and most of the places we've gone so far have been pretty wooded with no direct sun. Plus they're expensive.

 

[Gary RV_Wizard]

Jammer pretty well answered your questions.  The GC2 6v batteries happen to be the best available combination of capacity and price for a true deep cycle battery, but they do require series wiring instead of parallel and they are a different shape and height than your present SRM-24's (group 24 case size).

If you want more capacity in an existing battery, it has to be a larger size. There are a variety of standardized sizes and shapes available and you need to figure out what will fit in the battery box that you have. The site below has a list of standard BCI battery case sizes, their dimensions and the approximate amp-hours that can be stored in that size.
http://www.batterystuff.com/kb/tools/bci-battery-group-sizes.html

A "marine deep cycle" is a low cost hybrid of a engine starting battery and a deep cycle. They have about the same amp-hours as a true deep cycle battery but they don't last as long under repeated discharge and recharge cycles. A true deep cycle such as the GC2 golf cart battery is designed solely for deep cycle use and lasts 2x or more longer. Trojan, Deka and a few others make 12v batteries in a true deep cycle design, but they tend to be quite expensive because they are a low sales volume item. Since there are lots and lots of golf carts in use, the GC2 golf cart battery is produced in much higher volumes and thus are lower priced.

 

[tykesplace]

If I go with 2 GC2s I can handle the series wiring. I think i'd have to replace the box though. I was watching a youtube vid last night where the guy said that 4 GC2s in a parallel/series combination to get 12 volts is a great setup if you can afford the batteries and can handle the weight. The truck is a 1 ton so that's fine. The hitch says tongue weight limit is 500lbs, or 1000lbs "weight distributed" and I have a 10k lb equalizer hitch. The TT is a Keystone Hideout 31BHSWE and I think the hitch weight is 725lbs.

I think I'll shop for a couple of DC2s and see how that goes. Then maybe 2 more later if I need to.

 

[Jammer]

A "marine deep cycle" is a low cost hybrid of a engine starting battery and a deep cycle. They have about the same amp-hours as a true deep cycle battery but they don't last as long under repeated discharge and recharge cycles. A true deep cycle such as the GC2 golf cart battery is designed solely for deep cycle use and lasts 2x or more longer. Trojan, Deka and a few others make 12v batteries in a true deep cycle design, but they tend to be quite expensive because they are a low sales volume item. Since there are lots and lots of golf carts in use, the GC2 golf cart battery is produced in much higher volumes and thus are lower priced.

Unfortunately the terminology varies among manufacturers.

Exide makes a "marine deep cycle" group 24, 12 volt battery -- the NG-24 -- which is a true deep cycle battery that will perform as well as GC2s (aside from size and voltage differences).  They also make a "marine dual purpose" NC-24 and a "marine starting" XHD-M-24 battery.  I have every reason to believe these are actually different batteries and not just different stickers.  They make the NG "marine deep cycle" in group 27 as well, and possibly the others (but they're not stocked at my local store).  The NG batteries are a few bucks more than the others.

Interstate, as near as I can tell, doesn't make true deep cycle batteries.  I have their "deep cycle/marine" batteries in my Airstream (dealer put them there), and while they work OK for now, I'm skeptical of their performance and am planning to do a drain test on them this spring to see if they're doing their job.  Interstate makes it sound like these are true deep cycle batteries, but they're not.

Someone will probably come along soon and point out that these batteries come from the same factory, and perhaps they do, but you get what you specify and if the marketing gurus at Interstate don't specify deep cycle well that's that.

So you don't have to go to Trojan etc and get high-buck batteries just to get deep cycle performance, although you can, if you're willing to pay about 50% more than the going rate.

 

[tykesplace]

I just called the local Interstate. They have GC2 6v 235 amps for $130 each. They can also do the cables if I need them made. Sound like a good option? Maybe I can get something for my two batteries on craigslist.

 

[Jim Godward]

Sounds like a good price as I paid $105 4 years ago.  Check with a Freightliner dealer or a truck repair shop as you might just beat the Interstate price for the same exact battery.  I did and since I was a repeat customer, I got a price here in Belgrade.

 

[Mopar1973Man]

Odds are he now has Group 24 marine batteries, which means he about has 2 x 80 AH = 160 AH. Changing over to 2 x Group 27 deep cycles will yield about 2 x 105 AH = 210 AH or a  30% increase.  Changing to 2 x GC2 golf cart deep cycles yields 230 AH, or about a 45% increase. Close enough to 50% for saleman-speak!

Any of these had a usable Ah capacity of about 50% of the max rating. A bit less on the marine batteries and maybe a bit more of the golf cart batteries, but right around 50%.

Just to make you all scratch your head some more. Using Gary's info about and then comparing to my sticks and brick which is battery/inverter powered. I've got 820 Ah's worth of batteries. Eight 6V batteries on a 24 volt system. This is all hooked to a 4Kw inverter at 120 VAC. This combo I'm good for over 24 hours without a generator with normal living. So now getting back to the RV it about trying to find you power thieves and get them weeded out. Extra capacity is nice but reducing loads also works hand in hand in making the batteries last longer. I know the RV furnace is a big consumer. Greasing the blower bearings help drop the load/draw but creating a custom grease gun fitting for blower motor. Spins free now and faster. Like converting to LED's another way to save... But this another project.