The best OEM-style battery for a Mazda Miata is the WestCo battery, made specifically for the car. They are of compact size and sealed, since they are located in the trunk. Note that all of the Miata sealed batteries are have small hoses connected on the _ and - sides of the battery. This allows any battery fumes to be ventilated out of the car. An aftermarket sealed battery MAY have these small ports in a different location. You'll just need to go to your local Autoparts store to purchase an extra 1-2' so you can replace the old tubing. Should cost no more than a few dollars. View the related links below for WestCo.
This answer is applicable for 1990-2005 Mazda Miatas.
The battery is a Mt-MX5. This is a Interstate battery part#. fits 1990-2008 Mazda Miata. Go to interstatebattiers.com to find a dealer near you.
It uses a very small, sealed battery, because it resides in the trunk. The battery features ventilation ports that attach to tubes inside the Miata trunk so it is safely ventilated outside of the cabin. The most common replacement is a WestCo Battery, specifically designed for the Miata.
A small battery that fits in a key fob or remote.
Anyplace that sells batteries can tell you the correct size battery you need.
R12
Car batteries are quite universal. As long as the battery physically fits in the battery box it will work. When selecting a battery, get the battery with the highest cold cranking amps you can afford. The extra battery power helps the starter crank the engine over faster when it is cold.
The 2011 Mazda MX-5-Miata has a 5-speed manual.
The 2004 Mazda MX-5-Miata has a 5-speed manual.
The 2012 Mazda MX-5-Miata has a 5-speed manual.
The 2009 Mazda MX-5-Miata has a 5-speed manual.
The 2005 Mazda MX-5-Miata has a 5-speed manual.
The 2014 Mazda MX-5-Miata has a 5-speed manual.