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Hold Down for Optima Battery 6V

September 23, 2010 | Troubleshooting & Repair

By Linus Pauling, Jr.

Although the Optima battery has been around for several years, I did not acquire one until recently when I finally got my '65 Cabriolet ready for the road. The Optima represents a very significant advance in lead-acid technology (see Pat Tobin's article in 356 REGISTRY Volume 24 Number 3 ) and is perfectly suited to the needs of the owner who drives his car only occasionally. It does not spill acid, it has a very low self-discharge rate and its low internal resistance means more starting voltage, among other virtues.

The only problem with the Optima (besides initial cost) is that its shape is quite different from a standard battery, so the 356's hold-down system will not work. What I wanted is a system that utilizes the original placement, hold-down mechanism and cover.

The system I devised does that (see Photo 1, below) by using top and base plates made to fit the Optima's shape. This has worked well for me in two T6s. It also fits, with some adjustment, in the T5 (and presumably in the T2 also) battery compartment.

Making the Hold-Down

The top plate (on the right of Photo 2) is 1/8" hardboard also, 6 5/8" by 9", sized, with corners rounded on a 1" radius, to fit into the T6 cover. The holes for the terminals are 1 1/4 " diameter, cut with a hole saw.

Photo 2: The completed plates. The base plate is on the left, the top plate on the right. Both are made from hardboard. The base has laminated to it a plywood piece(s) cut for the shape of the Optima battery. See the text for dimensions, or the illustrations, following.

To make these pieces waterproof, I coated all surfaces with Gougeon West System 105/206 epoxy (from a marine supply store), but any brushable epoxy should do. They can then be painted black.

Installation of the Hold Down

Note there are small modifications to get the hold-down and battery to fit into the 356. See Photo 3, below, for the final assembly. Enjoy!

L-Bracket Modifications for the T6

Because this setup is about 1 " wider than the standard battery, for the T6 it may be necessary to drill and tap (8mm-1.25) another hole in the L-bracket at the floor to get the proper hold-down. No further adjustments are necessary.

Shelf or Hold Down Modifications for the T2 & T5

The fiberboard battery cover of T2/5 models has metal shelves inside. The one on the right (passenger side) will short out the 6+ terminal if they touch. To avoid that, the shelf can be shortened 1"or, alternatively, the spring hold-down can be replaced by a rubber band. The top plate may have to be relieved to clear the ground strap which goes under the shelf on the left.

Photo 3: The Optima Holder assembled, with Optima battery installed.

Illustrations for the base plate and top plate

1 Comment

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Conrad Carter
September 02, 2015 at 1:05 AM