battery-box

How I made a battery box

Background:

When I bought my car it had a stock Suzuki motorcycle battery installed. The battery was all of 12 Ahr and if the engine didn't start right away it would loose power very quickly. Since the motorcycle had twin headlights, dual tail lights and other electrical equipment similar to a car, I decided to use the battery till it went bad and replace it with something larger when the time came.

Well that time has come so I went to a few stores that sell Garden & Tractor batteries and found the most powerful one available (a 350 CCA battery). The new battery is "somewhat larger" than the motorcycle battery. The bigger battery in the picture below is not the new one but the one I used for sizing the battery box. Another deciding factor is that the tractor battery is about half the price of a motorcycle battery. (I explain why it was cheaper on the next edit entry.)

[5/7/2015 edit] The garden tractor battery lasted for about 3 starts and most of the cells shorted out!! Unfortunately the 90 day warranty ran out before I completed making the new battery box so I was stuck with it. A good example of "They don't make 'em like they used to."

If I don't start the engine for a week or so the engine is very hard to start because there is no way to choke the engine. You just have to depend upon the computer to set the starting mixture and fast idle speed.

To see an enlarged view of most pictures, left click on a picture or right click and select "View Image".

This is a top view of the area where the new battery will be mounted. The rectangular riveted plate is where the original battery was mounted. The hole was larger than the motorcycle battery to allow for the mounting bracket and the box it used hung down into the passengers foot well area!

The existing rivets presented a problem in mounting the new battery box because the surface is not flat.

This picture is out of sequence to show how the completed installation of the new battery fits and looks. The battery is mounted right in front of the relay rack. The relay rack cover is removable with the battery in place. If necessary, the whole battery box can be removed.

The red and blue battery cables are AWG #4. The cables are from the junk yard and were used to supply battery current to a high power car audio amplifier!

This is the piece of aluminum I used to make the sides of the battery box. It is 3-1/2" high with a 1/2" wide lip on the bottom. The thickness is 1/8".

The metal was very hard to bend without annealing it to soften it. I used the acetylene soot torch method.

To anneal the aluminum I adjusted my torch for a very sooty flame and coated the aluminum on both sides with a line of soot about 1" wide using pencil lines as a guide. You want the soot thick enough so you can't see the aluminum through it.

The vertical pencil line is where I want to end up with a 90° corner. The cross hatched area is metal that has to be removed so the fold can be made.

The round mark at the apex of the metal to be removed is where I will drill a 3/16" diameter hole before removing the metal. The next picture explains why.

After coating the vertical line with soot I adjusted the torch for a rather long "soft" blue flame and moved it in circles over the soot until I burned the soot away.

*** CAUTION ***

Do not overheat the aluminum! It WILL suddenly melt without warning if you overdo it. The idea is to apply just enough heat to burn the soot off but not heat the aluminum any more than necessary. The heat will be transfered to the metal as the soot burns away. What I do is heat the soot by moving the torch in 1" or 2" circles and when I see the soot starting to disappear I move the torch toward the other edge of the sooty metal (not the other side) to heat that side for awhile. Go back and forth until all the soot is removed where the fold will be (my pencil line). Don't heat the metal any more than necessary to remove the soot. I waited 15 seconds or so before burning the soot from the other side of the metal.

A few hints that might help:

Do not force cool the metal after removing the soot. Allow it to cool in the air.
Don't forget that when you decide what size the box needs to be you have to allow for some padding around the battery. I used an old rubber disk from a LP record player platter as padding for my battery box.
After doing the first 90° bend, carefully measure where your mark is in relation to the bend. You will probably find that the fold has eaten up some of the length you wanted. That is why one of my sides is ~1/8" too short. I found I had to add ~3/32" to my lengths. But it depends upon how small the radius your bend is.

Here is my first fold. Too bad the -last- fold didn't turn out as good. At least it can't be seen when the box is mounted. ;-)

Notice that the 3/16" diameter hole has been filled in by the folded metal. This allows a nice tight 90° corner.

I did not use a brake to bend the metal. I clamped the piece to be bent to the edge of a metal work/welding table (the 1/8" thick steel chassis of an old riding lawn mower) using a piece of 1/4" thick steel plate spaced ~1/8" from the pencil line where the bend was to be made. The pencil line overhung the edge of the table by 1/8".

I also clamped a hard wood 4" wide x 12" long flat handle to the part to be folded with more steel plates on either side of the aluminum. It was rather easy to bend the metal after annealing.

Here is the completely folded box. Oops, one side should have been 1/8" longer to narrow the gap.

I purposely designed the box so the open ends of metal would be located where I was going to put a vertical metal strips on either side of the box where the battery hold down would be located.

I've already drilled and counter sunk eight #6 holes for the mounting screws. The left and upper drilled edge in this view are mounted to the thin firewall metal that has no real strength. The 2 screws are used to keep the firewall from drumming against the bottom of the battery box.

The bottom and right side lips are directly over two 1" frame members under the firewall. I drilled and tapped the holes for 1/2" long #6 countersunk screws in the frame tubes. Using screws allows me to remove the battery box if necessary.

The white object is a wood spacer made from a piece of an overhead room fan blade. It is 1/4" thick. The metal box will sit on top of this wood.

I routed out circles on the underside where the firewall rivets are located to mount the firewall to the frame tubes etc. This produces a flat surface for the battery box to sit on.

The location had to be such that the box would clear the return fuel line from the pressure regulator and allow access to the relays. Lots of things to consider for a simple battery box.

This picture shows the folded battery box sitting on the white wood spacer during measurements.

It took a lot of careful measurements to make sure that I would be able to mount the box onto at least two frame tubes for safety.

I also cut out a rectangle of 1/8" thick veneer to fit inside the mounting lips of the box. This allows a completely flat surface for the battery to sit on.

The 1/2" diameter bolt is one of six that holds the engine mounting cage in the chassis!

Side view of completed battery box.

Before putting the battery into the box I inserted the rubber LP pad into the box.

Top view of battery box.

You can see the rubber strap with metal D rings on the ends that is used hold the battery in place. This strap is the original Suzuki battery hold down.