Dual 6V Batteries in a 2720SL

[mjlaupp]

It takes some carefull measurement but it can be done. I purchased a model GC2 Marine battery box from Allied Barttery Co. www.alliedbattery.com I had to seal the battery box wire cutouts with some plastic and hot glue, cut a drain hole and add the vent for the gasses. The new battery box is taller, wider and longer. I had to move the vent higher in the wall, that required a 3" hole saw. I was afraid of recessing the box into the floor because of the battery weight: 2 x 75 lbs. Yes, I have lost some of the storage space. The extra battery life more than makes up for it. I can leave the fridge set to 12v power with the fridge heat exhaust fan running all day without pulling the battery down.
MJL

[mjlaupp]

Here is a picture of the compartment after the modifications needed for the new batteries and battery box. I have filled the cutout in the floor with expanding foam with a drain pipe insalled. The wood blocks are to locate the box and prevent it sliding around. The U-bolts in the wood blocks go completely through the floor and are used to attach a cargo strap for battery hold down. The strap was crash tested on my '02 2720SL, it held the batteries in place even though the trailer was totaled. I also had to relocate the tube through the floor for the ground wires. It is now to the left of the wood block. The old hole is sealed with silicone.
MJL

[mjlaupp]

Here is a comparison picture of the standard battery and the new deep cycle golf cart batteries. Note that the golf cart batteries are viewed from the end and the standard battery is viewed from the side. I have made the modifications (sealed wire cutouts, added drain, added vent hose) to the new battery box in this picture.
MJL

[Bill]

Oooh, nice work! You got BOTH batteries into a single box? I like it!

Bill

[mjlaupp]

Originally Posted by Bill

Oooh, nice work! You got BOTH batteries into a single box? I like it!

You can get a model Long GC2 battery box from Allied Battery that holds 2 batteries end to end. I think it would work on most of the front battery mounting areas. Note that the new '04 2720SL has a larger storage area that is 3 inches deeper due to the shore-line storage area being moved to the bumper storage area. This modification would be much easier on the new models.

MJL

Originally Posted by mjlaupp

Here is a picture of the compartment after the modifications needed for the new batteries and battery box. I have filled the cutout in the floor with expanding foam with a drain pipe insalled. The wood blocks are to locate the box and prevent it sliding around. The U-bolts in the wood blocks go completely through the floor and are used to attach a cargo strap for battery hold down. The strap was crash tested on my '02 2720SL, it held the batteries in place even though the trailer was totaled. I also had to relocate the tube through the floor for the ground wires. It is now to the left of the wood block. The old hole is sealed with silicone.
MJL

MJL:
As a novice, and new owner of a used TM, hope you don’t mind a question or two regarding your project of installing 2 6v batteries. In reponse to an earlier posting I made, was referred over here to view your project. Must say it really looks neat and tidy based on the jpg.

My questions mostly range in the structure of the 2720sl.

From your picture, it appears you installed the u-bolts all the way through the flooring; as you state. On the TMs, I was ‘under the impression’ the floor is ‘lightly’ made of some material … like perhaps 2 sheets of plywood with the foam insulation between as depicted on the TM web site. Was it a simple job of just drilling down thru the inches (how many?) of the floor?

What was/is the purpose of the cavity; and was it really necessary? I presume in looking at the jpg that you merely dug out the previous floor area down to the bottom sheeting.

Did you also have to cut out a larger hole thru the floor for the drain pipe? And how is it held in place on a permanent basis? Theorize that if it is just held by the expanding foam, may loosen up and drop off.

Finally you mentioned you had to relocate the exhaust tube. Did that encompass cutting out a new hole in the rear of the TM? If so, what did you do to plug up the old outlet hole from outside ... used the old grill or what?

Thanks
doon

[mjlaupp]

Originally Posted by doonboggle

MJL:
As a novice, and new owner of a used TM, hope you don’t mind a question or two regarding your project of installing 2 6v batteries. In reponse to an earlier posting I made, was referred over here to view your project. Must say it really looks neat and tidy based on the jpg.
My questions mostly range in the structure of the 2720sl.

I located the new batteries in the rear compartment since that is where the original battery and battery box was located. I assume that yours are also located in this rear storage compartment and not on the tongue. Installing 2 batteries of this size in the rear compartment may be too much rear weight bias for safe towing if you have the rear mounted spare tire. My spare is located under the floor and ahead of the axle.

Originally Posted by doonboggle

From your picture, it appears you installed the u-bolts all the way through the flooring; as you state.

If you look closely at picture #2 you will see the curved end of the u-bolts with a metal plate between them and the wood. This is the flat plate that comes with the u-bolt. I put it there to prevent the u-bolt from sinking into the wood and loosening the bolts. I have 1x4 inch mending straps drilled for the u-bolts on the underside of the floor to prevent the u-bolts from tearing out of the floor.

Originally Posted by doonboggle

On the TMs, I was ‘under the impression’ the floor is ‘lightly’ made of some material … like perhaps 2 sheets of plywood with the foam insulation between as depicted on the TM web site. Was it a simple job of just drilling down thru the inches (how many?) of the floor?

The floor is a 3 inch thick sandwich with aluminum skin on the top and bottom. There is a very thin layer of plywood under the top aluminum skin. There is a 2x3 frame board in the floor under the rear wall of the rear wall. A drill just walks through this sandwich like a knife through hot butter.

Originally Posted by doonboggle

What was/is the purpose of the cavity; and was it really necessary? I presume in looking at the jpg that you merely dug out the previous floor area down to the bottom sheeting.

The cavity was put there by the factory. The original battery box was recessed into it. The bottom aluminum skin of the floor was left in place at the factory to help support the battery.

Originally Posted by doonboggle

Did you also have to cut out a larger hole thru the floor for the drain pipe? And how is it held in place on a permanent basis? Theorize that if it is just held by the expanding foam, may loosen up and drop off.

I used a piece of 1 1/2 inch schedule-40 PVC. It is imbedded in the expanding foam and held in place by the foam. If you have ever worked with expanding foam you would know that there is almost no chance of it letting go of the pipe. If you get that stuff on your hands, it has to wear off. Use disposible gloves when working with the foam.

Originally Posted by doonboggle

Finally you mentioned you had to relocate the exhaust tube. Did that encompass cutting out a new hole in the rear of the TM? If so, what did you do to plug up the old outlet hole from outside ... used the old grill or what?

I re-used the grill for the new hole. I cut the new hole with a 3 inch hole saw and glued the cut out core to fill the old hole. I cut a piece of plastic out of an old lid for an under-bed storage box lid to use to cover the old, filled hole. The box cover was chosen because it's color matched that of the vent cover. You can see this in the first picture. The home-made cover is below the vent and to the right of the door.

MJL

Originally Posted by mjlaupp

I located the new batteries in the rear compartment since that is where the original battery and battery box was located. I assume that yours are also located in this rear storage compartment and not on the tongue. Installing 2 batteries of this size in the rear compartment may be too much rear weight bias for safe towing if you have the rear mounted spare tire. My spare is located under the floor and ahead of the axle.

If you look closely at picture #2 you will see the curved end of the u-bolts with a metal plate between them and the wood. This is the flat plate that comes with the u-bolt. I put it there to prevent the u-bolt from sinking into the wood and loosening the bolts. I have 1x4 inch mending straps drilled for the u-bolts on the underside of the floor to prevent the u-bolts from tearing out of the floor.

The floor is a 3 inch thick sandwich with aluminum skin on the top and bottom. There is a very thin layer of plywood under the top aluminum skin. There is a 2x3 frame board in the floor under the rear wall of the rear wall. A drill just walks through this sandwich like a knife through hot butter.

The cavity was put there by the factory. The original battery box was recessed into it. The bottom aluminum skin of the floor was left in place at the factory to help support the battery.

I used a piece of 1 1/2 inch schedule-40 PVC. It is imbedded in the expanding foam and held in place by the foam. If you have ever worked with expanding foam you would know that there is almost no chance of it letting go of the pipe. If you get that stuff on your hands, it has to wear off. Use disposible gloves when working with the foam.

I re-used the grill for the new hole. I cut the new hole with a 3 inch hole saw and glued the cut out core to fill the old hole. I cut a piece of plastic out of an old lid for an under-bed storage box lid to use to cover the old, filled hole. The box cover was chosen because it's color matched that of the vent cover. You can see this in the first picture. The home-made cover is below the vent and to the right of the door.

MJL

If I understand the theory correctly, by putting the smaller batteries together, in series, one can extend the boondocking time element. The success you've posted raises another thought in my mind.

In looking at your installation, note there remains lots of room in the 2720sl rear battery compartment ... with just the two (2) batteries.

Recognizing the weight aspect, would more batteries also do MORE? In other words, if 2 batteries extend one's time element some xx hours, then would ... say 3 battteries extend the element some xxx hours, etc, etc..

Thanks
doon

[mjlaupp]

Yes, more batteries = more time. However they must be installed in matching sets:
1 - 12v battery or
2 - 6v batteries in series or
2 - 12v batteries in parallel or
4 - 6v batteries in series-parallel.
I would not install more than 2 of the golf cart batteries in the back compartment of the TM. The 2 batteries will weigh somewhere close to 150 pounds and that is a lot of weight to add anywhere in the TM. Adding more weight to the back will only make the TM prone to sway while towing. I don't know if I would want to add 4 batteries (=300#) at any location in the TM.
MJL

Great info and photos, mjlaupp.

My original TM 12-volt batteries are fading and I am going to replace them with 6-volt Interstate U2200 batteries. Your excellent posts on this topic have given me almost all of the information I need. My dual side-by-side battery box is on the way from Allied and I plan to abandon the cavity support method in favor of a strap like you used because my battery floor is already sagging a bit.

A few questions - I was under the impression that the battery box is supposed to be vented/drained on the bottom as well as the top and this is why you have the segment of PVC pipe down there in your foam. However, when I looked at my current situation, while the TM floor has a hole in it, the battery box supplied by the factory (or dealer?) does not - it is solid.

Should I cut a hole in the bottom of my new Allied battery box to match up with the drain hole/pipe, and if so, is it a completely open hole or a group of smaller ones? If the heavy battery is sitting directly on top of this hole, is anything able to get out, anyway?

Also, in retrospect, is there anything you would do differently if you were tackling this project today?

P.S. Yes, I do understand that I will have to wire the two 6-volt batteries differently than the two 12-volt ones - I have a diagram.

Thanks in advance for any suggestions.