Installing a WestCo / Miata battery in the Elise

[DesignIt]

When I went to replace my original battery in my ’05 Elise, the first place I went was the local Lotus dealer. They sold me an Interstate battery that had the positive and negative terminals reversed from what they should have been. In addition, it weighed considerably more than the original OEM battery and, like the OEM, was also a lead acid wet unit. I looked at the available batteries for the Elise and the excellent list compiled by TheViper, but didn’t find what I wanted: Battery Choices & Information

I ultimately decided to go with a WestCo AGM battery originally made for the Miata. I liked this battery because at 25lbs it was slightly lighter than the OEM, but it was still a full-size battery that would last for a while without recharging. It was also not a wet cell battery, and since I own a first-gen Miata I am familiar with the quality of this battery.

The WestCo specs are:
Amp hours 31
CCA 475
Length 7 ½”
Width 5”
Height 7”
Weight 25 lbs
Price $124.95 from WestCo

The first step in mounting this in the Elise was to build a battery box. The Miata has a nice clamp and J-hook arrangement to hold the battery in place, so I opted to design an aluminum battery box around those two parts. I also bought an Optimate trickle charger made by tecmate.com and hardwired the SAE-71 battery to charger quick connector to the Lotus battery cables. Here’s a quick pictorial of what I did to create the box:

I first made a quick paper template to get the correct dimensions for the mounting holes and hold down bracket.


The dimensions were then transferred to a more accurate paper template and chedked for fit.


Once I was satisfied with the fit I glued the templates onto a sheet of 6061 aluminum and cut out the brackets.


The bends in the main bracket have to be done in this order so that the part can be fit into the sheet metal brake, or vise. The back section is bent first.


Then the side flanges can be bent.


The locating / stiffening ribs were then bent into the J-hook bracket


Bending the center section of the J-hook bracket required a few spacers and a vice.


The last bend aligned the main bracket with the Miata hold down clamp.


Here's a slightly larger view of the finished battery box with the Miata hold down, the J-hook and a battery mat.


Battery box installed.


Battery and charging cable installed.


The final installation.


I attached the .pdf files if anyone wants to make one for themselves. These are full-size, so you should be able to glue them directly to the sheet metal and start cutting and bending. I also have this in AutoCad and Adobe Illustrator if anyone is interested. I hope this helps if anyone is looking for another battery option for the Elise.

John

[TheViper]

Nice Job
Cheers,
Michael

[DesignIt]

Thanks Michael. Hopefully someone can benefit from my prototype. There are no holes that have to be drilled in the body (This is a long-running trademark of my modifications, going way back to my early Miata days) and the bracket holds the battery very well.

I included the battery specs so that if you want to, you can add this to the battery chart that you posted.

Thanks again,
John

[TheViper]

John,
One thing that impresses me is that the battery terminals are secure from being shorted out, as is common with some of the designs I have seen. It scares the hell out of me to see bare or insufficiently insulated terminals that are just waiting for a major catastrophe by coming into contact with trunk contents.
Cheers,
Michael

Originally Posted by DesignIt

Thanks Michael. Hopefully someone can benefit from my prototype. There are no holes that have to be drilled in the body (This is a long-running trademark of my modifications, going way back to my early Miata days) and the bracket holds the battery very well.

I included the battery specs so that if you want to, you can add this to the battery chart that you posted.

Thanks again,
John

[mrcarcrazy]

John, I'm impressed. could someone with less tools than you convince you to make a second one? for a reasonable fee?

Can't blame me for trying.

[DesignIt]

mrcarcrazy,

Thanks for the compliment, but one is enough for me. I take way too much time to be able to charge a reasonable amount.

TheViper,

Thanks! I wanted a setup that would be very stable and could use factory Lotus battery cover. I'm also scared of having the battery contacts exposed. I've seen enough unintentional arc welding to last me a lifetime.

BTW, I updated the battery mount PDF to show the proper bending sequence.

John

[mrcarcrazy]

Well heck, can't blame me for trying. I may see if I can borrow a buddies shop to build one of these, once I get caught up on all my projects.

Thanks for making the PDF's. I'm really impressed by your work (I've been called easily entertained before...but still)

good work, and thanks