The Miata Battery

By Anthony Wilde

(Courtesy of the San Diego Miata Club)


More Choices Than Ever Before

Every Miata manufactured and sent to the U.S. since 1989 has been factory equipped with a special battery. I wrote an article for the SAN DIEGO MIATA CLUB NEWS in 1997 that detailed the stock Miata battery and an alternative aftermarket replacement (SDMC News, Volume 2, Number 6). This article is available on the SDMC Web site and on Miata.net in their respective Garage sections.

Since that article was written, changes have occurred in the area of batteries for the Miata. The OEM (original equipment) battery is a product of Panasonic. This battery caused confusion early in the sales of the Miata, since it did not require service like a standard car battery. In addition, mechanics who tried to "quick charge" it found out they quickly ruined it.

At the same time, Miata owners were finding out this is one great little battery. Usually a car battery will last, on average, 36 months. If you take good care of it, and live in a temperate  climate, 48 months might be expected. The Panasonic has a demonstrated average life of 6
years (72 months) and there are continuing reports of original Miata batteries still going strong beyond the 10th year of service. Still, people complained when they had to shell out $130 for a replacement from Mazda.

In mid 1998, Mazda quit selling the Panasonic battery as a replacement for the Miata. When you go to a Mazda parts department you now get a standard wet cell (albeit sealed) battery. The price is only around $80, but you will NEVER see 72 months of service from this battery. Mazda  claims this change in batteries was due to customer complaints about the original battery. Well, I cannot dispute that, but I believe that economics played a larger role. The Panasonic battery is made in Japan. In order to supply Mazda parts departments in the U.S. with batteries, they need to ship pallets of very heavy, thereby costly, batteries over the ocean. The new replacement is manufactured in the U.S. and is not subject to long ocean voyage transportation costs. That is why every Miata that enters the U.S. still carries a Panasonic battery in the trunk. No sense shipping U.S. made batteries to Japan!

Another strike against the new replacement battery from Mazda is one of commitment. The original design of the Miata placed the battery in the trunk for good weight distribution. This helped the handling of the car, as we all know, but it was not a place for a corrosive and possibly
explosive item like a car battery. That is why Mazda chose an Absorption Glass Mat (AGM) battery to be placed in the Miata. The AGM is a suspended electrolyte battery that ties up the battery acid in a fine fiberglass mesh and keeps it from spilling in your trunk. If this design was
important enough for the factory to install it (and they still do) then why should we accept less for a replacement battery?

Well, a lot of enthusiastic Miata owners do not accept less. WestCo has been providing a replacement AGM battery for the Miata since it had a 1.6 liter engine. This battery was cheaper than the Mazda Panasonic battery and still had the virtues of the OEM unit. One small drawback to the WestCo battery was the reversed battery terminals, in relation to the Panasonic battery. By turning the battery around when installing it this was negated, but the battery cables in the Miata
trunk were sometimes very short in this arrangement. WestCo changed this in 1999 and the terminals are now in the same orientation as the OEM battery. The cost of the new WestCo battery is $80 and it works just as advertised. I replaced my 7-year-old Panasonic unit with one in November 1999 and it is working just fine.

American Battery Corporation has introduced a new player to the Miata replacement battery scene. Their American Eagle battery is an AGM, just like the original Panasonic and the WestCo. In addition, it is slightly smaller in size. This smaller size is a good thing, since the terminals are reversed like the first generation WestCo. Since the battery is slightly smaller, the short cables are less of a problem when making the connections. SDMC member BRIAN GOODWIN has been using one of these batteries for several months in his '94 Miata and likes it very much. The list price for the American Eagle Battery is $80, same as the WestCo.

While the reversed terminals might seem to handicap the American Eagle battery, the specifications make up for it.

Battery Cranking amps
new (wet cell) Mazda 370
WestCo 475
American Eagle 530

As you can see, the American Eagle has the highest cranking amps of the three
replacement batteries. That, coupled with the discounted price of $59.90 to SAN
DIEGO MIATA CLUB members, makes the American Eagle battery worth considering
when your Panasonic finally dies of old age.

Either the American Eagle or the WestCo are deserving candidates as re-placements
for the Panasonic battery in your Miata. Accept nothing less.

- ANTHONY WILDE

American Battery Corporation
525 West Washington
Escondido CA 92025
(760) 746-8010

WestCo Battery Systems
Anaheim CA
1-800-214-8040
http://estorebc.mkbattery.com/Category/41_1/Miata.aspx


Note from Scott Thomas

Lately I've been doing some research because the stock AGM battery finally went out on my '95, and it seems that the only true AGM replacement batteries are the WestCo and the American Eagle. The current Mazda dealer replacement is a wet cell, so no good there. Today, I found another true AGM battery that is made specifically for the Miata. It's in the car now, has a slot on the top for the stock battery retainer pole, fits perfectly, and the battery terminals are in the correct location. This is an AGM battery, 370 cold cranking amps, 32 amp-hours (same as stock I believe), and has the same vent holes for the stock battery vents. The battery also comes with a 72 month replacement warranty, and costs $82 retail.

The battery is the Sure Start Miata, the part number for any parts store that carries the battery is SSB-MIATA. O'Reilly's and Autozone around here both carry them, so just about anyone should be able to get them.

So we've got another battery than the WestCo and American Eagle.


The battery in automobiles today is not far removed from the first lead-acid storage batteries developed in 1859 by Gaston Plante for use in telegraph equipment. An electrochemical process between the lead, lead dioxide and an aqueous solution of sulfuric acid, is constant. What has changed in the intervening years is the technology applied to better materials and advanced production methods.

If you knew about battery maintenance in 1947, the same procedures would be valid on automotive batteries in 1997. The liquid electrolyte, sulfuric acid, must be maintained by addition of water to replace the liquid that is boiled off during the charge and recharge cycles of normal use. The inevitable spill of acid on or around the battery would have to be cleaned to prevent corrosion of the metal. The battery posts would periodically need to be wire-brushed and cleaned to remove the corrosion present there as well.

Of course we do have maintenance-free batteries now, but the maintenance still seems to be required, and if you get 3 years on a car battery that seems pretty good. If you leave the lights on, or the battery doesn't want to crank the car over, just throw it on the battery charger for an hour or jump start the car and drive it around for a while. If that doesn't work, toss in a new one.

Along comes the Miata, and things change. As retro as the Miata was intended to be in styling, the electrical problems that were common in the British roadsters of days past, were not in the plan. Since the Miata was meant to drive, and not to work on, the battery had to be as reliable as the rest of the car.

In a normal lead-acid battery, the electrolyte is sulfuric acid in sufficient quantity to cover the lead plates in each battery cell. This type of battery is referred to as a wet or flooded cell battery. The main drawback to this type of battery is the continued maintenance and possibility of spillage of acid during maintenance or an accident.

About 1958, attempts were made to immobilize or fix the electrolyte in the cell of the battery using various methods. One of these was to use silica gel to bind the water present in the electrolyte solution into a jelly. Just imagine a battery full of cherry JELL-O. These type of batteries are used in many applications and are referred to as gel cells.

For the record, the Miata battery is NOT A GEL CELL.

In 1985, when the Miata was taking shape in Irvine, a new battery technology was being used in military aircraft. The paramount considerations of power, weight, safety, and reliability were the selling points of this new type of battery. The new technology was AGM or Absorption Glass Mat. This technology was an evolution of previous battery technologies, including gel cells.

In AGM sealed batteries, the acid is absorbed between the lead plates and immobilized by a very fine fiberglass mat. This glass mat absorbs and immobilizes the acid while still keeping the acid available to the plates. This allows fast reaction between the acid and plate material. The intimate relationship of the electrolyte-filled mat and the lead plate, allows the construction of a smaller battery, using less electrolyte and metal plates. This means a smaller battery with nearly equal power ratings to a wet-cell battery of larger size and weight.

This Miata battery uses the AGM technology and is manufactured by the Panasonic battery division of Matsushita Battery Industrial of Japan. The Panasonic battery can only be purchased through Mazda dealers.

A replacement battery is also offered by a company in Anaheim, virtually in the shadow of Anaheim stadium. WestCo (1-800-214-8040), offers a battery of the same AGM technology as the stock battery.

The WestCo battery has a rating of 475 cold cranking amps (CCA) to the stock batteries' 440 CCA. As far as capacity, the WestCo is 35 amp hours vs the stock 32.

The Panasonic battery is vented to the outside of the trunk through a small rubber hose. This vent removes the hydrogen gas that can accumulate inside any battery during use. The amount of hydrogen developed during the use of an AGM battery is quite small when compared to a wet-cell battery. The WestCo battery does not have any vent, as it is sealed. WestCo claims the gas generation is so small, that venting is not required.

The only real difference in the two batteries is price. The Panasonic battery can be obtained for about $129 at Mazda dealers. Of course, this does not take into account any discount for being a San Diego Miata Club member. Check the newsletter for participating dealers. Due to the original classification of this battery for shipment, it can not be shipped via UPS.

WestCo sells their battery through many of the vendors of Miata accessories, such as Dealer Alternative, Moss Motors and Imparts. They also sell the battery direct through their Anaheim facility. For $84.95, minus the 5% discount for Miata Club members, the WestCo battery is very enticing.

The only real difficulty with the WestCo battery is the terminal posts. The posts are reversed, as to polarity, when compared to the Panasonic battery. This will cause an interference with some aftermarket power antennas, due to the length of the battery cables, so check with WestCo first. Several club members use the WestCo battery with no problems.

How will you know if you need a new battery? With most cars, a jump start and driving around will bring a low battery back. Try that with a Miata and chances are you will think the battery is history. Not so fast!!

One of the differences with the AGM battery compared to the wet-cell battery is the recharge rate. That is, how fast you can put energy back into the battery. With a wet-cell battery you can "quick charge" it at about 20 amps or more. Usually this is when you would boil the electrolyte right out of the battery. The AGM batteries require a lower charge rate, for a longer time period. If your battery will not crank the engine, you should charge the battery at a rate of 1 amp or less for 18-24 hours. If you try and charge it like a wet-cell battery, you will destroy the battery.

Those of us who enjoy our Miatas everyday-it's our only car-usually don't have a problem with the battery going flat, unless we leave the lights on. Those who only get the opportunity to drive their Miata on weekends sometime will encounter a low charge on the battery. This is due to the constant electrical load, known as dark current, on modern automobiles. The memory for the clock, radio stations, engine computer all take small amounts of power from the battery. Those who add alarm systems, etc. might have a greater dark current than stock.

WestCo has a small battery charger for the Miata for those who drive their car infrequently. The Accumate LS6/1.2 is a great little charger that will automatically maintain the charge in the battery. The advantage of this charger is you can leave it plugged in and it will not overcharge the Miata battery.

Some people might think that the easier solution would be to put a conventional wet-cell battery into the Miata. Indeed there are battery manufacturers who sell wet batteries for our beloved roadster. Before you go down this road, consider the dangers involved.

The generation of hydrogen gas in a wet-cell battery is much greater than in the AGM battery. Even those batteries that are vented still have the problem with all that liquid in the trunk. The potential for corrosion in this area is very great. Battery acid on your luggage and clothing would not be too cool either. In a rear end collision, the potential for the battery to crack open and spill, or possibly explode, should not be discounted. When you consider the cost of a good wet-cell battery is nearly that of the WestCo battery, the justification for putting a wet-cell battery in the Miata really makes no sense. It is false economy.

Some manufacturers are even pushing wheelchair batteries for replacement in the Miata! I don't think I like the connection.

Overall, the original Miata battery and the WestCo replacement are quality products that fit the Miata like a string-back driving glove. This is the first car I have owned where the only battery maintenance I perform is to dust the top of the battery every year. Several club members have batteries that are 6 or more years old that are still performing well. When you factor this into even the non-discounted price of the Panasonic battery, that is only $21 a year. About the cost of 1 tank of supreme unleaded.


Back to Electrical

12 March, 2014