I would like to reduce the tongue weight of our 2009 WW FB2100. There are currently 2 6v batteries mounted on a rack on the tongue. There is enough depth at the rear to mount them under the bed of the trailer in the center near the spare tire. I can make access plates in the bed of the trailer for 2 drop in battery boxes. The boxes would be vented underneath and I know the requirements for cable sizing. I've been searching for an in-floor mount/drop-in style battery box, but haven't found much. Has anyone seen anything like that? In a few weeks I'm going to set up a lever scale to measure the tongue weight and shift the batteries to the rear for a second measure before cutting any holes. I'm thinking moving the batteries from 11ft in front of the wheels to 4ft behind has got to have some effect. It would be a more secure location for the batteries and still be accessible.

You need to vent the top, Hydrogen will not vent downward since Hydrogen is lighter than air. Introducing Hydrogen into your living area is a bad idea. Play with the scale some, you're really not going to save that much weight, if you are over capacity you need to consider other options IMHO.

Y-Guy wrote:You need to vent the top, Hydrogen will not vent downward since Hydrogen is lighter than air. Introducing Hydrogen into your living area is a bad idea. Play with the scale some, you're really not going to save that much weight, if you are over capacity you need to consider other options IMHO.I was thinking to not actually mount the box in the floor, but under it. The box would not be sealed with lots of holes for venting, solid in front for rock damage protection. An access hole in the floor would be edged with metal, sealed with a gasket and screwed down. This is similar to older class-Cs with the battery under the floor that have a flip up panel for access in the steps.I think the tongue weight is just under max. My calculations show about 100lbs off the tongue.

All that work to save 100 lbs?? Not worth it IMHO

Toys reduce tongue weight and enough tongue weight is important to eliminate sway.I'd leave the batteries alone.

What is your tow vehicle? 1/2 or 3/4 ton?I agree on moving the batteries wont accomplish much. What is your WD hitch setup and is it undersized?

Relocate batteries to reduce tongue weight | Good Sam Community

31 Replies

misterpowertool
Explorer
Nov 18, 2014
RTBabich wrote:
misterpowertools wrote:
... The first trailer had a 758# TW on a 3330# empty TT. The second TT had a 864# TW on a #4300 empty TT. Excessive for both. I have borrowed a 1000# scale to find this out. First TT got a group 31 diehard platinum under the sink, barely fwd of the axles. Second TT got 2 Exide group 31 AGMs in a rear storage compartment. ...
What were the tongue weights after the rework?

First TT 758 to about 680lbs had two 24s, got one 31
Second TT 864 to 740 lbs had two 24s, got two 31s

Those cheapy 24s were OK for a friends trolling motor, one went to an enclosed trailer, another is the starting battery in my gas golf cart.
RTBabich
Explorer
Nov 17, 2014
misterpowertools wrote:
... The first trailer had a 758# TW on a 3330# empty TT. The second TT had a 864# TW on a #4300 empty TT. Excessive for both. I have borrowed a 1000# scale to find this out. First TT got a group 31 diehard platinum under the sink, barely fwd of the axles. Second TT got 2 Exide group 31 AGMs in a rear storage compartment. ...
What were the tongue weights after the rework?
big_buford
Explorer
Nov 16, 2014
Strabo wrote:
I towed our 5vr yesterday to the repair shop, it was empty.

No water
No Rhino
No food
No firewood
No clothing, gear

I was surprised how heavy it still felt...

The trailer itself was much lighter, but a properly designed fiver (toyhauler) the pin weight goes way up when unloaded. Mine is the same, it is a wierd feeling.
misterpowertool
Explorer
Nov 16, 2014
I did nearly the same thing to my last 2 travel trailers and will likely do it to my current toy hauler before spring. On the travel trailers, I ditched the el cheapo batteries that came with them and bought some nice sealed big AGM batteries. The first trailer had a 758# TW on a 3330# empty TT. The second TT had a 864# TW on a #4300 empty TT. Excessive for both. I have borrowed a 1000# scale to find this out. First TT got a group 31 diehard platinum under the sink, barely fwd of the axles. Second TT got 2 Exide group 31 AGMs in a rear storage compartment. Neither were hard at all to rewire and I did upsize the wire even though they moved closer to the converter. For what you might spend on access doors and undermounts, you might be close to the cost of some sealed batteries and save yourself some work.
Strabo
Explorer
Nov 07, 2014
I towed our 5vr yesterday to the repair shop, it was empty.

No water
No Rhino
No food
No firewood
No clothing, gear

I was surprised how heavy it still felt...
FireGuard
Explorer II
Nov 06, 2014
If you want precise calculations you need to find the center of balance C/B of the trailer.
Then take the weight and multiply it by the distance from the C/B to get the moment.
The C/B wont be the axel location, it will be much farther forward.
I was a Loadmaster on a C130 cargo plane and made these computations many times.
In my opinion, I don't think it would be worth the effort.
Now, in my case to keep the A/C within limits we had to, but for a trailer I wouldn't worry about it. Just carry all the stuff in the rear and watch how full your tanks are.
1L243
Explorer II
Nov 06, 2014
It looks like your guessing on the TW with what the trailer plate says? That figure could be way off. You really need to weigh in now (fully loaded) before you do an modifications to reduce TW. At 750lbs of TW (after moving batteries) and a almost 9000lb trailer is going to be flirting with sway issues. Weigh in get your numbers then you will know where you stand... Relocate the batteries for security or access but not to reduce TW. It could actually make towing worse. If the Expy is dragging due to TW make your mods there not in the trailer. Airbags would be my choice...
http://www.youtube.com/watch?v=WMYyA4w0kAs
RTBabich
Explorer
Nov 06, 2014
Hap Hazard wrote:
... I strongly suggest you (he) locate a pilot and do some calculations. Every pilot must know weight and balance for his aircraft. They measure the distance from the center of gravity to the location of the weight. Using a formula they can determine the new center of gravity. By proper loading they can shift the center of gravity forward or back.
It sound like you’ll be removing nearly 100% of the weight from the forward position but only shifting a small portion of that weight behind the axle. To be most effective you should move that weight as far back as you can to accomplish your desired hitch weight.

I used to know a few pilots. I worked on the F-14 software for many years. It is correct that 100% of the weight would be removed from the forward position and another 100% would be removed from the tongue if I could put them 11ft behind the axles. However, there is only 4ft behind the axles. Even 80lbs off the tongue would be good. This is not an airplane, it's a teeter totter. I was only looking at a possibility for lowering the tongue weight on my Expy as it is close to it's max in case loading for a trip is different than normal. I have done approximate calculations and it looked interesting. When I get the trailer loaded normally after a couple of trips I will weigh the tongue, then place the batteries temporarily in the back and reweigh. That will give me exact info.
Hap_Hazard
Explorer
Nov 06, 2014
There’s more to this story. RTBabich states he wishes to move the batteries from 11 feet ahead of the axles to 4 feet behind. I strongly suggest you (he) locate a pilot and do some calculations. Every pilot must know weight and balance for his aircraft. They measure the distance from the center of gravity to the location of the weight. Using a formula they can determine the new center of gravity. By proper loading they can shift the center of gravity forward or back.

It sound like you’ll be removing nearly 100% of the weight from the forward position but only shifting a small portion of that weight behind the axle. To be most effective you should move that weight as far back as you can to accomplish your desired hitch weight.

Hap
RTBabich
Explorer
Nov 05, 2014
otrfun wrote:
... Curious, what is the current length and gauge of cable from your converter to your batteries? Will the length increase or decrease by moving the batteries? FWIW, cable size (gauge) is typically undersized (restrictive) on most OEM installations. If you’re going to rerun the cable I would consider using a larger gauge cable. This could reduce electrical losses and decrease charge times.

The converter is an Inteli-Power 9100 40A. The output has 2 wires. One wire is 8ga which goes to a fuse block with six 12ga leads from it. The other is 10ga going to the batteries about 10ft long.