Battery Box Extension
From the threads I’ve seen on this forum, it appears quite a few of us have modified our battery boxes to accommodate larger batteries for dry camping or boondocking (or at least are thinking about it). I found some info on the forum about fitting larger batteries, but not much and not enough details to tell me how folks modified the battery box. So I decided to use my engineering background to custom design my own modification. In this thread I’m providing the details of my design including instructions and pictures of the install. I have the drawings for the extension and lid that I provided to a local sheet metal shop to fabricate the parts. I will make them available on the classified portion of this Forum – look for “Battery Box Extension Plans.” If you use my plans, check the overall size of your battery box first to ensure my design fits your box. Also, some Airstreams have a front storage door, so this raised box won’t work (there are threads of a “lowered” box on the Forum.
My AS battery box, like most I presume, is sized for two Group 24 batteries which fit with some room to spare. Group 27s however, are at best a tight fit since the front and aft flange on the battery box is bent inwards which reduces the opening by two inches total over the size of the box’s inside dimension. The Group 27 battery dimensions I found online (most around 12 ¾ long) didn’t appear to me to fit in the current battery box opening (13 1/2 inside but 11 5/8 opening). Plus there isn’t much space above the batteries. My modification does several things that accommodate both larger (like grp 27) and taller (like 6V) batteries. It removes the fwd flange and attaches the hinge differently to increase the opening by 1”; and it adds 2 ½ inches in height. In addition to accommodating taller batteries, the additional height is helpful to house a shunt and additional wiring for a battery monitor like the Trimetric (an important dry camping item that is my next project). I plan to mount the shunt to the face of one of the extension C channels – but that’s another project and thread.
PIC 1 is where I started - the standard factory battery box with Group 24s installed.
PIC 2 is the extension I designed. It is made of 3 C channels (aft, L & R) that are 2 ½ inches tall, and one flat side which is designed to mount to the fwd side of the box where the current box flange is removed. At 2 ½ inches tall, the top edge of the extension does come fairly close to the front surface of the AS – but it does fit and the lid opens with clearance. I designed the extension to be made from bent sheet metal (one or multiple pieces) or a weldment. The shop I used to fab the extension elected for a weldment, which looks very good and blends right in with the existing box. I had it made from stainless steel – I specified anything from 0.050 – 0.060 thick. Before installation, I sanded and degreased the bare metal, then primed the parts with RustOleum spray primer and painted them with RustOleum spray enamel. Use multiple thin coats to avoid pesky runs.
First I attached the extension to the battery box. To install the extension on the battery box I drilled out the rivets attaching the current lid to the box, then drilled out more rivets to separate the lid and hinge. The lid is scrap, the hinge is reused. Then I used a reciprocating saw with a metal blade to cut off the fwd battery box flange as close to the box as possible while being careful not to damage the finish on the box. Then use a file to smooth the rough edge. Cutting on my beautiful AS was the scariest part of the entire process! (PIC 3 – we’re committed now!) I pre-drilled the rivet holes in the flanges of the extension, then clamped the extension to the battery box and match drilled holes in the aft, L & R box flanges (PIC 4). The fwd piece of the extension rivets to the fwd face of the battery box. On this side of the extension I pre-drilled the rivet holes in the extension, then match drilled the holes in the battery box. I used blind rivets and installed them “wet” for corrosion resistance by first placing some enamel paint in the holes.
Next I placed the lid and hinge in place, drilled holes in the front side of the box extension to match the hinge, and riveted the hinge to the extension. I designed a new lid since it needed to be approximately 1 inch longer than the old one due to the flange on the battery box being trimmed off to give me the larger opening size I wanted. With the hinge attached to the extension (PIC 5), I aligned the lid on the box, drilled the rivet holes in the lid to match the hinge and installed the rivets. I installed these rivets wet too, although the hinge itself is not painted. The sheet metal fab shop forgot to put the lip on the aft flange, so I’m going to look for a key locking latch that will work with the thickness of the door and flange.
To finish up, I will install the latch on the new lid, touch up the paint on the extension as needed, and then sit back and admire my newly modified battery box (pic 6 and 7). Tons more room now!
I hope this helps some of you out there who have been considering this type of upgrade to your AS.
Have fun and be SAFE!