Mazda Miata Battery (1999–2005 NB) — Deka 8AMU1R Sealed AGM

This is the exact-fit battery for the 1999–2005 NB Mazda Miata — the Deka 8AMU1R, a Group U1R sealed AGM. It drops into the Miata's trunk tray, secures with the factory hold-down, and uses the correct reversed-terminal layout so it matches your cables. Made in the USA, ships fully charged, 1-year free-replacement warranty.

The NB was the second-generation Miata — the fixed-headlight car that arrived for 1999 (the US skipped a 1998 model year) and ran through 2005, including the 2001 refresh often called the NB2. Despite the restyle, Mazda kept the battery in the trunk and kept the same Group U1R fitment, so a single battery covers every NB model year.

Build features:

This is the Deka 8AMU1R, a genuine Deka (East Penn) battery made in the USA. It's a U1R — the reversed-terminal version with the positive post on the left — so it lines up with the Miata's cables. A standard U1 will fight the connection.

What this battery fits

Every 1999–2005 NB Miata uses this battery, including the 2001-and-later NB2, mounted in the trunk on the passenger side. Not sure which generation you have? The NB has fixed headlights; the 1990–1997 NA has pop-up headlights and takes the same battery listed for the NA.

Why a sealed AGM — and AGM vs. lithium

Because the battery sits in the trunk, just behind the cabin, a sealed AGM is the right type, and that's practical, not marketing. It can't leak acid or vent gas the way a flooded battery can, it shrugs off vibration, and it holds its charge better when the car sits — which most Miatas do.

You'll also see lithium batteries marketed for weight savings. Here's the honest tradeoff: lithium is lighter and costs more, and it's worth a look if you're chasing every pound for competition. For a street Miata, a sealed AGM like the 8AMU1R is the practical pick — sealed, trunk-safe, dependable in the cold, and far easier on the wallet.

About the 8AMU1R for your NB Miata

It's a starting battery, so it's rated by cranking power and reserve rather than amp-hours: 320 CCA, 400 CA, and a 45-minute reserve capacity. That's plenty for the Miata's small four-cylinder in any climate you'll drive it — comfortable margin without paying for overkill. (If you ever see a specific amp-hour figure quoted for this battery, treat it as an estimate; Deka doesn't publish one.)

A Miata battery typically lasts 4 to 6 years. The biggest variable is how the car is stored, and since Miatas sit, keeping it on a maintainer between drives is the single best thing for its life.

How to install it

About a 10-minute job, no special tools.

1. Open the trunk and lift the passenger-side cover panel to reach the battery.
2. Disconnect the negative terminal first, then the positive.
3. Release the factory hold-down and lift the old battery out. Keep it for recycling — most auto parts stores take SLA batteries at no charge.
4. Set the 8AMU1R in, minding the U1R reversed terminals (positive on the left) so the posts line up with your cables.
5. Reconnect the positive first, then the negative, and re-secure the hold-down snugly. A loose battery in a trunk is a real hazard.

How to make it last

Keep it on a maintainer between drives, don't leave it sitting dead, and it'll see the long end of that 4-to-6-year range. The full rundown — size and group, why it's an AGM, fitment by year, and the swap — is in the guide.

Frequently asked questions

Not sure it fits your car? Send us your year or call 1-877-775-4381 — we'd rather point you to the right battery than sell you the wrong one.