Battery Experiment - Mazda/Healey

[Dave Russell]

Over the years I have tried several different battery arrangements. The BN1, BN2, originally used two 6 volt type 17L batteries located in "boxes" on either side of the drive shaft. The BN6, BN7 used the taller 17H battery.

The late BN1 through BN7 had a somewhat restricted battery length due to the larger rear axle housing that was used. 17H batteries will fit the available footprint & their additional height will still barely fit into the available space of the BN1, BN2. Fortunately, the later Healeys with trunk (boot) mounted batteries have more available space so that an Optima or other sealed battery can be used.

With traditional 17H batteries becoming scarce & expensive, to say nothing of the "mess" created by wet batteries, I looked for a better arrangement.

The Mazda MX-5 Miata batteries were originally made by Panasonic & are an "Absorbent Glass Mat" construction. Completely sealed, compact, & sturdy. Reportedly, some MX-5's were equipped with the more conventional wet cells by USA dealers, presumably because of lower cost & lack of availability of the Panasonic.

Westco has been supplying Miata batteries with "AGM" construction. It is the same technology as used in the Optima batteries. https://www.batteryweb.com/miata.cfm

I decided to try the Westco #12V31M AGM battery in place of the two 17HF batteries. Specs are:
Length - 7 1/2"
Width - 5 1/4"
Height to top of terminals - 7 1/4""
Weight - 25 lbs
CCA - 475
AH capacity - 32
Price - $85

The 17 HF batteries:
Length - 7 3/4"
Width - 6 3/4"
Height to top of terminals - 9 1/2"
Weight - 30 lbs each
CCA - 300
AH capacity - 100
Price - $140 each

The higher CCA of the AGM battery provides very quick starting. While the reserve capacity of the new 12V31M battery is only about 1/3 of the original 17HF, it has provided to be more than adequate so far, in moderately cold temperatures. It likely wouldn't do so well in sub zero temperatures.

A new top hold down was made from 1/4" diameter rods & .060 steel end pieces.

It does get rid of 35 pounds of weight, all of the maintenance, & all of the acid leakage/corrosion mess, & is much cheaper. See attached pic---
D

 

[Keoke]

HI Dave, Ifin it was me I would use two of the Mazda Batteries in Parallel. 32 AH capacity just might not get you home if the charging system fails.---Keoke

 

[Dave Russell]

I considered it. Going to try it with a single. My alternator never fails. Good fall back remedy though.
D

 

[Bob Claffie]

A real plus is the long life of the Miata type batteries. The original battery in my '92 Miata lasted ELEVEN years (car is driven eight months a year, but no winter usage). The Westco replacement is now at four years with no deterioration noted. Bob

 

[zblu]

Have thought of doing same with 2 in parallel, any probs?, still using old genny

 

[Keoke]

zblu, where the Dynamo is being used I would seriously consider paralleling the batteries.---Fwiw--Keoke