First, the question must be answered as to why someone might consider installing a battery that is physically larger and of a different type than that specified for their vehicle. The answer is to increase total available current and battery longevity. If you install a larger starting battery, you will end up with more Cold Cranking Amps and more Reserve Capacity than you would get with a smaller battery of similar quality. If you install a larger Starting/Deep Cycle or Deep Cycle battery, you will get a very durable battery with a much higher RC and about the same or perhaps somewhat fewer CCAs. The battery will also probably last longer as deep cycle batteries have thicker plates with more active material. If your Mazda is equipped with a lot of power hungry equipment, installing a larger battery can provide more current and increase RC, without adding a second battery.

There are also reasons not to do this that should be considered: [ol][*]Starting/deep cycle and 12 volt deep cycle batteries do not come with as long a warranty as do high quality starting batteries. This should NOT be taken as an indicator of reduced longevity for a deep cycle battery in an automotive application however, as these batteries are normally subjected to very deep cycling in their intended application, which is very hard on any lead-acid battery. Also, these batteries are often subjected to long periods of storage without charging, which leads to a much reduced service life from sulfation. This is why deep cycle batteries do not have long warranties. If they are cared for properly, they can last just as long or longer than a starting battery. In automotive use batteries are seldom cycled deeply, so a deep cycle battery should actually last longer in most cases than a starting battery, provided that you add distilled water as needed.[*]Starting/deep cycle or deep cycle batteries require periodic watering with distilled water. If you want to avoid having to add water, either forget going with a deep cycle or get one of the new spiral plate, sealed AGM starting/deep cycle batteries like an Optima Blue Top.[*]In order to install a larger battery, you will likely have to perform some modifications to your vehicles battery mounting hardware. You must ensure that the hood does not contact the positive battery post, even when it is dropped or slammed shut, not only to prevent any possibility of shorting, but to prevent denting of the hood as well. You must also make sure the battery does not shift or vibrate excessively. [/ol]
If you decide to install a larger battery, get the very next size up. Make sure the larger size can fit with your existing mounting hardware (unlikely) or with modifications. Getting it to fit usually requires modifications and/or replacement of the mounting hardware (tray, hold down bracket, J bolts etc.). You might also need to use metal brackets to to fill gaps and ensure that the battery is held in place. The polarity of the terminals of the larger battery might be opposite to that of the battery you are replacing, requiring you to mount the new battery with the terminals 180 degrees from the position of the terminals of your current battery. If the positive terminal of the battery includes a threaded stud in addition to a post, it is a good ideal to insulate or cover it to prevent accidental shorting or shock.

Finally, if you choose to go with a deep cycle, select a battery that is made to handle a certain amount of shock and vibration, like a marine/RV battery. Do not get a battery intended for a stationary application, like renewable energy storage, as these batteries are not made to handle the vibration and shock that an automotive battery is subjected to.

I installed a Trojan 24TM starting/deep cycle marine/RV battery in my 2003 Protege and am happy I did, despite the fact that I had to make a lot of rather tedious modifications in order to get it to fit securely.


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A few other things to consider when replacing a battery are:

1.the type of posts (top, side or combination mounts,)
2.the location of the posts (which side of the case they are on)
3. (similar to 2.) and the polarity(+= right, -= left, or += left, -= right, forexample.)

Nice write-up protegedon!!

 

Thanks. It would have been better if I would have photographed the modifications as I was performing them, but I didn't think about posting what I did here until after I had partially completed it.

With regard to the terminals, the deep cycle battery I installed had the positive terminal on the right and the negative on left, which is opposite of the original battery terminal configuration. That is why I had to install it facing the opposite direction of the original battery. Marine/RV dual purpose (starting/deep cycle) batteries like the one I installed come with what are referred to as dual terminals, with posts that meet the automotive standard.
Since my post to the Protege forum, I epoxied metal corner brackets to the tray at each corner to keep the battery from shifting. I left about a millimeter to spare in length and width to allow for expansion and contraction and make it easier to remove and reinstall the battery in the future.
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one word... OPTIMA. Those things are bullet proof and well worth their weight in gold. I've sworn by them for years, and although expensive, they've never left me stranded. I run a 1000cca red top in my race car and a 34/78 series in my truck. Theyre as dependable as it gets.

 

From what I've heard, Optima batteries perform exceptionally well and are very durable. I know a guy here in Sacramento who installed a Blue Top in his VW Bus and loves it. With our mild winters, that was a smart choice, as reserve capacity is more important than a really high CCA rating.

One of the reasons I chose my Trojan battery, was the fact that it's a flooded battery with accessible cell caps so I can add distilled water as needed, which probably won't be too often. I plan to check it ever couple of months until I get a feel for how much water it loses through evaporation and hydrolysis. As long as I keep the plates covered with electrolyte, by adding water as needed, my battery should last a very long time. I might perform an equalizing charge every year or so to prevent stratification. Some people I talked to think my battery could last more than a decade.

Optima batteries are AGM, so you never have to add water and you can mount them in any position. However, it is my understanding that a well maintained, high quality flooded battery usually will outlast an AGM. This is especially true in really hot climates and it gets quite hot here in the summer (105°F or even higher). On the other hand, 5 years is plenty long enough for a battery to last in the minds of most. [align=left] [/align]