I bought my Miata in 2004 and had the original battery for almost 13 years. The original was an AGM which has an absorbent fiberglass mat sandwiched between the plates so the battery doesn’t spill/leak. It’s also more compact and more light weight than a regular car battery and fits in a small mounting area in the trunk to help balance the car and give it it’s 50/50 balanced weight distribution.
I wasn’t really aware that the old battery was on its way out. It still started pretty well and had never broken down. But I recently bought a large touch screen double din stereo and, after installing it, the clock would reset every time I started the car. I was completely confounded; couldn’t find any sensible reason for it and was actually quite frustrated after pulling everything out and checking the wiring and finding nothing wrong.
Eventually I saw someone online mention that a weak battery might be pulling too much power to crank the engine might sag and not produce enough power to run the stereo causing the clock to lose standby power and reset. I was a little dubious because a 1.2v coin battery probably has enough juice to run the clock. But I had tried everything else and the battery was about 13 years old.
I ordered the battery on Amazon for $100. Most local stored don’t carry small AGM batteries and have them on special order only. The local store that did carry one had it priced for about 40% more. Besides, I’m pretty handy and didn’t need help installing it.
The battery shipped for free, arrived quickly and was packaged sturdily in a box. On opening the box it was intact, no spills with plastic caps on the conductive terminal posts.
I installed it pretty much as soon as I got it. Install was pretty straight forward. You need a wrench to remove a single bolt that holds down the battery and loosen the clamps on the wires. Like the original battery, it is still vented and there is a hose assembly in the car that vents out of the side of the trunk. It’s important to reuse the vents because the vapor that escapes is corrosive and, with nowhere to go, it is very corrosive and potentially explosive, though I haven’t heard of anything serious happening. Check out the Porsche 914 to get some idea.
You can reuse the old hose even though the routing is slightly different, but so long as you have some cutters and some common sense you can cut a single piece of tubing and use the existing T connector to make it fit around the new battery. The posts are in the correct location and it all clamps back down no problem and the battery arrived pre-charged.
The first time I started up the car I noticed the difference immediately. Over 13 years I hadn’t really noticed the engine cranking slowing down. But the new battery made the whole car come alive with some shaking and it started very strongly. The other good news was that my clock was no longer resetting when I started the engine.
It’s been about 2 months now since I got the battery and it has been perfect. No problems whatsoever. It starts fine, cranks quickly, no odd electrical behavior. The headlights don’t dim at all when the engine settles to resting rpms when stationary or the AC compressor kicks in. I guess I should have read the signs but when it happens slowly over 13 years you don’t.
So to conclude, the battery worked a treat and I’m very happy with it. Highly recommended.
Good quality stock replacement
Product Name: MAZDA Miata Car Battery Deka/East Penn 8AMU1R AGM