The MGA With An Attitude

At 04:47 PM 12/28/05, Roger Bailey wrote:
>"You requested photos of the new Miata-sized battery, as installed. If you look carefully you can almost see the method of holding the battery securely. I have a 1/4" rod running across the battery, held rather conveniently by an existing 1/4" slot in the battery top. I 'kluged ' a couple of L-brackets to make a universal swivel to adapt the standard battery rods (which were shortened down) to the cross rod.
gel cell battery installed, left side gel cell battery installed, right side
Under the battery you can see the sponge pad on top of a plywood plate, used to lift the battery clear of the tray lip and ensure the battery case is properly supported. I used materials that will soak up vibration, but with an AGM it really isn't needed. The battery is mounted on the passenger side simply because it's cooler away from the exhaust, but again, the AGM probably won't care.

The thing it probably DOES care about is the excessive MGA charging voltage. As I mentioned some months ago, I am dealing with that by running with the headlights on, but I have a design brewing to deal with this issue automatically. On the other hand, I know one fellow who has a Miata battery and seems to get good service, even though he has no clue about charge rates, and has no instrumentation. He just runs the car - but admittedly not as many hours as I do, nor in as high an ambient. But I must find out from him though whether it is the 'real McCoy' AGM he has installed, or just the maintenance-free substitute that our local Mazda dealer is 'slipping' to the unwary customer. Mine, as you can see is not the official Mazda Panasonic issue.

Meantime, I can confirm that after several months of not being started, the charge level was still very high, and the car turned over very well, especially given how cold my sump-full of 20W50 was at the time. AGM's are supposed to hold charge much better over time than normal liquid L-A's, and they do. The smaller size / reduced capacity was not noticeable while starting yesterday, even after I didn't have enough choke!"


More comments from Roger:

This AGM battery was purchased from O'Reilly Auto Parts, a chain like Autozone and Advance Auto. The nearest branch to you appears to be Rockford area; nothing mapped to Chicagoland. It is an "SSB Super Start 72", size 26. You can find this 7.5" x 5" x 7" size-26 battery also made by Westco ( as a 12V31M rated 474 CCA, 31 AH. Also Marathon type MAR 8AMUIR.

East Penn Mfrg Co has a line called Gel-Tech. The model 8G24 offers 410 CCA and 132 RA, but the case is 10 7/8" L x 6 3/4" W and 9 7/8" H. The height might be a problem unless taken care of by the tray rewelding work. Other applicable Web sites include: and I wouldn't be surprised if one manufacturer was responsible for a number of labels.

FIT: You are correct: the battery is not a perfect fit. Unless one is willing to rework the tray (which I was not), the dimensions require that the battery be turned 90 degs lengthwise. The length is then about 1/4" more than the bottom of the tray which, as you know, is flared around the top edges. I raised the battery up to almost the top of the flair. The battery case is still immovable when clamped down, and the entire bottom of the case is in contact. There is plenty of overhead clearance under the cockpit lid.

Flimsy 1/4" rod: The thought occurred to me, too, but the rod is relatively short, and it snicks into a ready-made 200 deg enclosed slot. (I am sure that the slot is actually metric). The rod is threaded/nutted at the ends into brackets that are themselves threaded / nutted to the diagonal clamp rods, so it cannot go anywhere. The force required to shear it off would be immense. On the bright side, the battery won't leak acid.

12 Volt single versus twin 6's: The incentive/motivation for the change had nothing to do with a desire to go to a single 12volt battery. There is no economic or even really practical way to replace the aggravating liquid LA 6-volters with AGM's, at least, none that I could find. For example, Optima makes a 6 volt gel battery that costs twice as much as I paid for my 12v AGM, and the 'form factor' is all wrong. Also, it is a marine/auto hybrid design. Even at the 12 volt level, they do not make a 12v that will fit without a modified tray. Gel-Tech offers a 6 volt with a whopping 585 CCA 345 RA, but the tray has to be extensively modified and the cost is over $200. The 12 volt was used only because it is (presently) the only practical solution.

My original liquid LA batteries came from Moss. The batteries began to leak and fail over a 2 + year period, but never simultaneously. With these, and also the replacements, the pitch-sealed tops would split and leak, corrosion became a battle. I played around with various soft shock absorbing materials, but all batteries created corrosion and/or failed prematurely. I replaced each one with NAPA's. Seemingly different manufacturer, but same problems. NAPA no longer offers 17HF's, citing too many problems and low demand. Bought next ones from Interstate. Same issues. Interstate no longer offers the 17HF, same reasons. Found ONE different mfrs type on the Web... Oops! : Discontinued.

Part of the reason for these failures is design/manufacture, no doubt, but it is also true that the regulator dehydrates the batteries quite fast. The MGA battery location is not ideal from a vibration or heat point of view. Topping up is a frequent issue, especially in hot southern weather, and taking the lid off is a pain.

Another minor gripe is that liquid L/A batteries don't hold charge well for extended idle periods. Seeing the water levels is annoying, and cleaning off cauliflowers of corrosion is awkward and time consuming, anticorrosion sprays notwithstanding. If the battery itself is in decline, this high charge-rate results in ever more rapid depletion. The combination of all factors has led to many hundreds of dollars being spent. Hence the motivation to find a solution.

The ideal solution would be a battery that doesn't mind the temperature, couldn't care less about the vibration, can't leak or corrode, should last 5 years, and costs no more - preferably less - than the now hard to find LA type. I paid $90 for my AGM and replaced two $66 units. OK, I spent $10 on some new cable, and had to make a hold down bracket etc. AGM would be a perfect solution if overcharging was not an issue, but clearly, manufacturers are concerned about creating voids in the gel since, unlike a L/A battery gels cannot be allowed to gas.

The MGA needs a better regulator regardless of battery type, but the ability to limit long-term voltage levels while recovering after a start is probably a bigger factor with AGM's. That is IF you care about the economics AS WELL as the zero-maintenance benefits. My goal was to spend less than $132 (I did) and NEVER have to worry about the battery again for 5 years.

Cheers! - Roger
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