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Old 09-23-2019, 02:17 PM   #1
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Radical thought? Relocating batteries to rear

I just had a somewhat radical thought. Back in the day, it was common for high school hot rodders to relocate their batteries to the trunk to move more weight to the rear of a vehicle as part of changes to more evenly distribute weight front to rear. On my trailer, the batteries are at the tongue like 99% of all trailers, but in mine the DC distribution panel is all the way at the far back corner of the trailer, roughly 28' from the batteries as the cable runs (I have a rear kitchen model). So there is this anemic 6ga wire to deliver the 55 amp DC charging power to the battery all that distance away at the tongue.

So with that in mind, here is my question.

Does it not make sense to relocate my battery boxes to the rear bumper (assuming it is adequate to carry that load)? The battery would be 2 feet from the converter and DC panel then. Yes, I know there is a requirement for a battery at the front of the electric brake system to power the break-a-way switch and brakes. But that requirement can be met with a fairly small sealed battery and still meet highway "code". I would still keep a Harbor Freight tongue box up front to house the smaller battery and give tool, landing pad and blocking storage (and free up space in my pass through). I doubt it make much difference in the overall tongue weight. It would in theory also shorten the electrical resistance run from the battery to the various DC lights and appliances as well, especially any towards the front of the unit where you have that 28' run to the panel and then another 20' or more run back to the front on an even smaller gauge wire.

Most of the trailers I've seen have the DC/AC panel converter either in rear or rear 1/3 of the unit. It would seem logical for them to have the batteries at the rear as a matter of design (and would save on copper cable expense?). Even 2 group 31 lead acid batteries would only add 120 pounds total and AGM or lithium would be much less in weight. If a rear bumper can handle a bike rack or spare tire as a factory option, surely it can handle a battery box or two especially if mounted over the side frame extension and the bumper.

Another peeve I have is why do they not have some sort of access panel on the outside side bodies to the water pump, DC/AC and other areas for service? I'm not talking about a door like a storage door, but a ridged panel that has to be unbolted and is weather tight for service access only (and insulated). We have them on boats but not RV's and TT's. Servicing things inside cabinets and under appliances (which is where there is usually dead space to put those items) is a pain (literally - as you have to contort to get 2 hands in there while laying on your side or back usually). A exterior side access panel would make it so easy to winterize, and service these items and things like EMS units behind the DC/AC panel, damaged water lines, etc...
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Old 09-24-2019, 12:30 AM   #2
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Rethinking this.

One side of my dinette has the furnace under it and the other has nothing but lift up storage. I think I'm going to put 2 group 31 AGM batteries under there and modify the remaining space for a slide out drawer from the end of the dinette bench for easy access storage. AGM's are truly sealed, so no adding water, off gassing or need to vent the compartment outside when charging.

That makes the run to the DC panel & converter about 6' total and I can shorten the existing 6 ga cable to still run to the front of the trailer to feed just the brakes/break-a-way. That makes both runs more in line with the amperage that might be required. Plus the batteries are more protected from summer heat and winter cold (even in storage).

I can still keep the steel storage box on the tongue for 100% storage (which keeps weight on the tongue close to the same and the batteries will be directly over the rear axle near the side frame rail if I move them to the dinette base, so no added stress on the frame at the rear bumper area).

I'm thinking this is almost a no brainer as that is unused space under the dinette now.
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Old 09-24-2019, 12:37 AM   #3
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I am doing the opposite- I'm adding a converter to the front of the camper, right near the batteries. I'll go from 30-35' to 3. Plus, it's a lithium aware charger.

The only concerns I'd have for you is the weight distribution. Make sure you end up staying within the 10-15% of tongue weight and that the batteries are protected. Putting the batteries into the dinette is adding even more weight to that passenger-side (with the fridge over there).

Putting the batteries at the extreme rear may subject them to more jostling as the rig bounces. I don't know if that's a problem. But since you're not talking about that any longer, it's less of a concern.
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Old 09-24-2019, 01:06 AM   #4
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The spare is still up front and I have a lot of stuff in the pass through and under the bed. If anything it will make the hitch weight more in line, but I will weigh before and after. I can just pull the battery and get a "after" weight before the box install since the new batteries will be over one of the axles they should not tilt the weight distribution fore or aft overall.

I also am adding a hotel closet sized safe in the bottom of the ward on the opposite side of the trailer to secure our computers and other items if we go out. It's at least the weight of one of the batteries (AGM group 31's I'm looking at are 56 pounds each). Another plus is AGM's can be drawn down 80% where as the existing lead acid is only 50%. Not that I intend on drawing it that low. I may just put in one group 31 AGM to start but I have plenty of space for the 2nd. Current tongue battery is a group 24 lead acid wet cell deep cycle. I can use it in my boat as I have one that is getting old and flaky there.

This is what I'm talking about doing. Drawing shows 2 AGM's, but I can always start with 1 as I'm not really dry camping any now days and I have 2 honda EU 2000's with a parallel kit if I do.

Batteries will be protected with a manually trippable bussman marine breaker as the main. It can also serve as a disconnect. I also have some 4ga wire than I can upgrade the short run to the DC distribution buss with. I have a PD replacement/upgrade from the WFCO and the terminal can handle up to 4ga wire according to PD. Should be virtually no resistive loss on that short of a run with that gauge.

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Old 09-24-2019, 01:32 AM   #5
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Another thought about weight.

I could put the batteries towards the centerline of the trailer under that dinette seat. Then put a access door in the back side of the dinette base that opens towards the walkway at the fridge and entry. Another option would be to split the plywood under the cushion and have one side hinged and the other fixed by screws over the batteries with a divider wall between (make two compartments, both top access). Like I said, right now I'm not using that under seat space at all so it would be for infrequent use items and that would locate the batteries much closer to the centerline of the trailer and still be over the axle for fore and aft weight balance.

Might not really matter though?
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Old 09-24-2019, 05:28 AM   #6
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Weight aside venting the batteries to the outside could be an issue if placing them under the dinette seat. The fumes / off gassing would be extremely dangerous to the occupants.

Also if moving the batteries be sure they are connected to the emergency brake system. Not sure of the requirements of location, or possible inspection.


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Old 09-24-2019, 05:40 AM   #7
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Originally Posted by Oaklevel View Post
Weight aside venting the batteries to the outside could be an issue if placing them under the dinette seat. The fumes / off gassing would be extremely dangerous to the occupants.


Don't think AGM's require venting. Not sure.
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Old 09-24-2019, 10:45 AM   #8
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Don't think AGM's require venting. Not sure.
Me either, but can anyone guarantee the the current ACMs would always be replaced with ACM's
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Old 09-24-2019, 12:44 PM   #9
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AGM's do not require venting and do not off gas hydrogen or anything. The prohibitions against a totally sealed compartment are more for the potential of heat buildup during charging (rapid charging of a drained unit mostly). With no hydrogen off gassing, there is no reason I could not vent for heating to the interior of the trailer with 2 vents (one low and one high for natural convection flow in, across and out of the compartment).

As to ensuring no one ever places a conventional battery in there, What????? You can't ensure what anyone else will do about anything in the future. That rule was for manufacturers and is no different that all the other myriad of mods owners do to their rigs post purchase (new or used). For example, can you ensure that a future owner will not try to tow a 12,000 lb rig with a 1980 Ford Ranger via bumper pull? Nope....

For the sake of argument, I can easily mount a notice "WARNING - replace with AGM type sealed batteries ONLY", in the compartment on the lid.

As to the brakes, yes I would use the existing 6ga wire to feed a brake distribution buss and the break-a-way switch. It would have power from both the internal battery and the tow vehicle feed as power sources (which will also provide some charging while towing). Worst case, I could locate a smaller dedicated AGM battery inside the tongue box just for break-a-way power, but power is power. As long as adequate power is available to the device, it cares not the source or location of the source.
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Old 09-24-2019, 01:43 PM   #10
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I like your plan for under the dinette seat. If the safe you are installing offsets the weight of at least one battery side to side balance shouldn't be an issue. As far as shifting weight towards the back, it depends on what your current tongue weight is. If you are like me, 300 lbs over recommended tongue weight, moving the batteries back will balance the trailer. When I upgrade to a new trailer in a few years I plan on putting lithium batteries in the exact place you want to put your AGMs.
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Old 09-24-2019, 05:40 PM   #11
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Current battery is group 24 deep cycle (wet cell), so even a single group 31 AGM is about a 25-30% increase in capacity over current setup. I'm thinking put in one group 31, but build the compartment to hold 2. Plus the short runs to the converter should help with any wire resistance losses on that original long run.

The bulk of the storage in this unit is forward of the axles, so I'm thinking moving a single battery will not matter much (remember I'm also replacing the battery box with a good sized lockable tongue storage box so I may not have any weight change at the tongue once it's loaded with the jack pads, etc...

This a video of a similar tongue box install on a TT, but that owner kept his batteries in his new box. I'm going to use mine for increased storage to get some items out of the pass through. $89 at Harbor Freight, or $72 with the 20% discount coupons if not on sale (sale is usually $69).


My setup is a little different than his. I already have a spare under the tongue, so my battery cross members are above the frame instead of under. I'll just fill in with a pressure treated board cut to fit in the 2 steel "L" brackets instead of cutting and welding flush (spacer board adds a little weight back too) and then bolt the box through it and the metal cross members on mine. Like I said, mine will be pure storage (unless the law says I have to have a small break-a-way battery withing "X" feet of the break-a-way switch - in which case I will just add a small motorsports AGM in that box by adding a side divider. If someone knows of such a law please provide an actual cite - the break-a-way will be fed back to the AGM 31 in the trailer via retasking the existing 6 ga cable if not).

Remember, I'm just installing the box, not the batteries like in that video (that guy needs to strap his battery in, not just hold it with the side bracket or the bare terminals will ground out on the top of the box as the trailer bounces down the road). So it's a box illustration of the idea in my plan.
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Old 09-27-2019, 10:49 PM   #12
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I like the idea of moving the battery back to the dinette. Plus extra storage for stuff in the front. Jay
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Old 09-28-2019, 11:25 PM   #13
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I've been thinking about this a little further. My remaining concern is the break-a-way switch. Does anyone know if there is any code or law (as in you could get a ticket for) not having the battery within "X" feet of the break-a-way switch?

I'm thinking, just use the existing 6ga wire (which will be shortened to the new run) from the new battery location inside the dinette to the front of the trailer where the break-a-way switch is located. Plenty of power for brakes in an emergency. Same feed could also power the 30amp power jack line and take the tow vehicle charge line to the battery. In my thinking everything else can be moved back to the battery compartment inside the trailer for easy access (there is currently a 30amp self resetting breaker that feeds the slideout motor from the tongue, I would move it and greatly shorten that wire run as well). Basically the 7-way connector, break-a-way and tongue jack are the only DC wires that need to be at the tongue.

Other concern is there needs to be some fusing on that 6ga wire. I'm thinking 50amp self resetting would be fine. The jack has it's own 30amp fuse inline near the head, and if the brakes are pulling 50amps, there is a dead short to ground and I have no brakes with or without the break-a-way (which would also blow the fuse in the tow vehicle for 0% brakes left).

Other option is to put a smaller battery in the tongue storage box dedicated to break-a-way switch. My concern there is charging it from the converter/tow vehicle via the 6ga line in parallel with the main battery. I would think I will need isolation diode if I have them in parallel. Don't want the trailer pulling down the break-a-way battery for any reason. Other concern is charging them in parallel even through a diode. If main battery is way down and break-a-way is not (assuming they are both AGM chemistry), how will charging be affected by the 55 amp Progressive multi-stage converter/charger. I guess I could add a dedicated AC/DC charger for the tongue battery (small one).

If I can just use the existing 6ga to feed DC to the tongue and power the break-a-way and the jack, it is so much simpler as there is just one battery and one charging circuit. I just don't want the DOT doing a spot check and saying the battery is too far from the switch (electrically it's all the same though). Although I really can't imagine the DOR spot checking a 24' lightweight trailer, but some threads here seem to indicate they do check RV trailers occasionally.
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Old 09-29-2019, 09:53 PM   #14
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There is no rule about batteries distance from breakaway switch. The existing #6 wire will feed the jack and breakaway just fine. If its easy run a second #6 from the new battery location to the front of the trailer to help with a little voltage drop from the tv but it wont help much. Cutting the distance from the converter to the AGM batteries will really help a lot. Jay
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Old 09-30-2019, 01:39 PM   #15
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One option not mentioned (at least I didn't notice if it was) is to merely leave battery(s) where they are and increase the wire size connecting battery positive to Converter.

No construction, modification, etc. Just look to see what the maximum wire size your Converter panel will accept and go with that. My WFCO 8955 fuse block will accept up to a 1/0 wire size at the battery connection lug. If yours won't accept wire this large you can purchase "adapters" that will fit in the lug and take much larger wire. The short length shouldn't create any issues as the resistance is very low at that short a length.

1/0 welding cable will run around $3.50 per foot but will handle plenty of current especially compared to the #6 awg wire currently used. The 1/0 wire has less than 1/4 the resistance per foot than the #6.

If you do choose this route don't forget to upgrade the negative wires where they connect to the chassis. I did this with my TT and rather than just a ring connector fastened to the frame with small sheet metal screw I installed regular electrical panel lugs, attached to the frame with self tapping bolts. Also sanded all paint off the contact surface and used some No Ox Id grease to keep rust/corrosion from forming between frame and lug.

Unless you really need to shift weight the "wire" solution could well be less expensive and less hassle.

Just tossing this in for consideration.
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Old 10-01-2019, 01:11 PM   #16
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I had considered increasing the wire gauge, but I wanted a tongue storage box. Storage of the jack pads, bottle jack, misc blocking, etc... can be dirty and moving them to the box instead of keeping them in the slide through made sense. I don't think I will loose much if any tongue weight after I install the box and put it to use. Looking at the 2.3 cu/ft Harbor Freight Haul Master steel box ($89). My current setup has angle iron tack welded on top of steel tubing to hold battery boxes (tubing has the lift for the spare). If I cut a few welds and take the angle off, I have a nice flat strong steel tubing base to bolt the box to.

Also moving the battery inside a more temp moderate zone (AGM only!!!!) seemed to make a lot of sense. Other than the break-a-way switch and the tongue jack, everything else powered by the battery feeds from the rear of the unit, even the power to the slide out which will be about 4' away from the new location (as opposed to the 15' run now). And I'll increase the wire gauge to 2ga to the DC panel/converter from the battery with the relocate (along with ground). It will be about a 5 to 6' run after move so that with a larger gauge wire should be awesome for charging and power to the DC panel. According to PD, their WFCO upgrade kit can accept up to a 2 gauge wire so i should be good.

I'll start with 1 AGM but will build the space for expansion to 2. We don't boondock now, but I have before in a prior trailer so I know about power management and I still have my pair of Honda EU2000 generators and a parallel kit (can provide 33amps in parallel for full trailer operation). Looking at the Duracell AGM Group 31 (made by East Penn - Deka for Sam's Club), with 105 amp/hour capacity for this mod. I'll move the existing group 24 deep cycle (wet cell) to my fishing boat to replace a failing battery there.
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Old 10-01-2019, 01:39 PM   #17
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This a video of a similar tongue box install on a TT, but that owner kept his batteries in his new box. I'm going to use mine for increased storage to get some items out of the pass through. $89 at Harbor Freight, or $72 with the 20% discount coupons if not on sale (sale is usually $69).
I installed a tongue box on my trailer... I found some nice aluminum boxes at Lowes. i USED THE ONE SHOWN BELOW because of clearance issues with the WDH frame hitch and the fact that my hybrid bulges out on the lower section meaning I needed to move box forward to be able to open the lid... as you can see the bottom is smaller then the top. This has worked well for me and still has enough room to house a group 27 battery inside, plus chocks, wood pads, and tools in the trays at the top of the box.
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Old 10-01-2019, 02:15 PM   #18
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I did what Titan Mike suggested to our unit. Instead of changing the #6 wire to a bigger gauge, I just ran #8 wire that I had in parallel. I also upgraded the grounds. I calculated that the #6&8 wire together was just slightly more wire than #4. My power box is about an 19or 20 run of wire to the batteries. I measured before and after voltage. There was a big difference in how fast the batteries voltage equaled the converter voltage. (13.6). At the time I was running 3 group 31 dual purpose batteries. If I end up with a Coachman Freedom Express 246RKS like dward 51 has I will do the same thing with 1or2 AGM batteries. For me one of the dislikes of the 246 is one side of the dinette is taken by the furnace and the other side has no door for easy access to the storage under the seat. This seems like a perfect solution. Jay.
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Old 10-02-2019, 10:18 PM   #19
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Jay,

If I do this, I'm probably going to make the compartment for up to 2 batteries on the center line side of the dinette seat. I will install a divider (which will also add support to the seat section. I'll probably cut a storage opening on the back of the outboard side of the dinette (just inside the door) and install either a cabinet door or a sliding drawer on ball bearing full extension slides. Of course I will add supports to the back side of the area where the cut is made to support the seat. That will give a great storage area that is easy to reach by just opening door. Another good place to put items mostly used outside the trailer - just open the door and that new compartment is at chest level. Right now it's just a thought to utilize some currently wasted space.

I just need fall to actually get here. We have had like 82 days with temps 90* or higher. It was 98 at the house again today (October 2nd). IT's just too damn hot to work outside on the trailer (30 amp is at other end of house where I park the trailer - right now it's in the driveway and I'm working on the axles so I can't move it - so NO AC for working inside). I mean What's up with this heat???????
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Old 10-02-2019, 10:49 PM   #20
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As I read, some key points come up. Moving weight, increasing capacity (usable), modifications/construction, etc.

Adding the cost of a couple AGM batteries, wiring costs, construction materials, etc, and one is real close to the cost of a single 100AH LiFePo battery. 1/4 the weight of two AGM's, twice the usable power as most single AGM's, faster charging, and probably the last battery you'll purchase other than add a second one later if you install a big inverter.

Just tossing this into the mix.

FWIW, LiFePo batteries can be installed anywhere and really don't require access unless you want to show them to a friend.
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