View Full Version : SR20DET battery specs

06-13-2022, 01:52 AM
Its time to replace the battery for my s14 sr20.
I can't manage to find enough information about the recommended battery specs. My last battery was 12v 75Amps but I'm not sure if 75 amps is really needed or lower amp battery will work the same

06-13-2022, 10:43 AM
Starting batteries are usually selected by group size. Most batteries within a group will have similar specs within a few percent, more expensive batteries will be better, but it's mostly about what fits the car for us SR/KA/CA guys. Our engines don't need lots of cranking amps. The SR doesn't put any special demands on the starting battery. Not like the starter motor has to fight against the turbo. It's a low compression 2.0L four cylinder. Some people run crappy lawn tractor batteries (not suggested for cold weather).

The OEM spec reserve capacity of 75Ah basically doesn't matter at all unless you're running a big stereo or racing with no alternator or something. Any battery with enough cranking amps to turn the starter will have enough reserve capacity.


The factory battery is I think a group 24 (probably where the 75Ah spec comes from) which is unnecessarily huge. Especially if you don't drive your car in the dead of winter. And of course won't fit with an FMIC unless relocated to the back.

U1R size Miata battery will fit up front with most FMICs and start an SR or KA in any realistic weather condition. A U1R can happily start a '01-'05 Miata with a high compression (10.5:1) 1.8L in the dead of winter in factory torture testing. Something like an Odyssey PC925 will work and is even smaller. Both of these have way less than 75Ah reserve capacity.

06-13-2022, 12:08 PM
In 2002 my friend Finn put a lawn and tractor battery on his S14 sr20det 240sx.

rofl it could crank up the first time but it wouldn't go twice in a row without a little run time.

Still amazing $20 battery for a lawn mower started that thing.

These days I recommend might maxx battery from Ebay. You can get a $40 or $60 battery that will last 5+ years, Its a Sealed Lead Acid, I bought a couple 5 years ago and they crank over V8 engine and 4-cylinder no issue. Still great shape.

06-13-2022, 12:44 PM
Those Mighty Max batteries are just ATV/SxS batteries, which is pretty much what Odyssey and Braille batteries are, just with 'premium' construction and a longer warranty. But the actual specs are nearly the same.

A 'YIX30L' battery which is a replacement for various ATVs and Harleys has basically the same specs as a Miata battery in terms of capacity/cranking amps, it's just a different shape. I almost got one of those for my car as it's basically exactly half the size and weight of the stock battery. Odyssey PC925L is the same size. The biggest Harleys now have 1.9L engines!

06-14-2022, 11:24 AM
The JDM S14 comes with a "B19" sized battery. Which is roughly a 35Ah spec battery. It turned out to be a big pain to find JDM batteries with the skinny JIS pencil posts in the US, so after taking a bunch of measurements the U1R battery is the same size. I can use the JDM battery bracket, and it fits sideways to allow for FMIC piping to pass thru. Down side is that I had to convert to normal US battery terminals.