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Old 01-03-2012, 09:59 PM   #1
Road Geezer
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2011 27' FB Flying Cloud
San Jose , California
Join Date: Jan 2011
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Upgrading Battery Capacity

Over the holidays I swapped out my two grp 24s for a pair of grp 27s. If you're "metal-working tool-challenged" like me, you may have avoided this upgrade because the typical grp 27 battery can't be "shoe horned" into the battery box mounted in the A frame in later model Airstreams. Mine is a 2011. It turns out the the box is big enough to accommodate two grp 27s, but the opening under the cover is too short by about 1/2' to let them lower into the box.

I found it really quite easy to modify the battery box. Step-by-step here's what I did.

1. Remove the propane tanks and their housing to gain easy access to the box.
2. Drill out the three pop rivets securing the door hinge to the battery box. Remove the cover with its hinge and set aside.
3. Disconnect and remove the installed grp 24s. Note: Make a wiring diagram first. Remove the plastic pan if there is one.

The idea is to remove the top flange from only one end of the battery box. I chose to remove the front flange. The result will be an opening just over 13" wide. That's enough to allow slipping in the grp 27. It's tight but easy.

4. I outfitted my circular saw with a $4 fiber metal cutting blade. Note: WEAR eye and ear protection.
5. Center the saw and line the blade up with the inside edge of the front battery box panel. It's a bit of a guess. Turn on the saw, hold it firmly, and gently let the blade grind a slot in the flange. Don't force it. When the blade has bottomed out, gently guide the saw forward, then backward to cut off the flange. Note: this is one of the loudest noises I've ever made; protect your ears! Also, there will be a shower of molten metal sparks, don't try to look around the saw's blade protector if you're curious when it's cutting. The sparks are REALLY hot.
Don't worry if the cut isn't exactly straight, you can easily dress it with a file.
6. I attached a 1" strip of strap aluminum to the cover to extend it's length to about 14". I then reattached the hinge to the front face of the vertical front wall of the battery box. You can use machine screws with nuts or pop rivets. Attaching the hinge this way allows a full 13" opening. The cover then will rest when closed on the rear flange. Cool.

I haven't gotten around to figuring out how the make a little catch to engage the doodad that keeps the cover closed.

7. Install the new batteries and reconnect according to your wiring diagram.

I was allowing a whole day for this, but it actually took my less than three hours start to finish. My calcs tell me that I should gain about 40% more capacity; enough to get me thru a cold night with interior lights on and the heater set to toasty warm.


As far as I know, this is the oldest I've ever been.
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Old 01-03-2012, 10:28 PM   #2
Rivet Master

2005 25' Safari
Salem , Oregon
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Hi, I haven't measured my battery box, but it looks like the group 27's would fit, as is. I was also wondering if Airstream had a plastic tray to fit the 27's. Sure would be nice to see pictures of your modification.


2005 Safari 25-B
"Le Petit Chateau Argent"
[ Small Silver Castle ]
2000 Navigator / 2014 F-150 Eco-Boost / Equal-i-zer / P-3
YAMAHA 2400 / AIR #12144
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Old 01-04-2012, 12:23 AM   #3
Road Geezer
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2011 27' FB Flying Cloud
San Jose , California
Join Date: Jan 2011
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Just measure the opening with the cover open. If it's 13", the 27 will fit. My opening was just over 12 1/2" and I could slide in the 27 if I cut off the tabs that held the carrying handle. I didn't want to do that, so I opted to widen the opening. You can make the tray fit if you cut out the ends. The 27s are the same height and width as the 24s, just a bit longer.
As far as I know, this is the oldest I've ever been.
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