The Miata's battery lives in the trunk, on the passenger/right side - not under the hood. That is the first thing that trips people up when a Miata will not start.
Care:
- It is a small battery and is typically tired after about four to five years; it is sensitive to cold and to a parasitic drain.
- Keep the terminals clean and the hold-down tight - a loose battery bouncing in the trunk is dangerous and shortens its life.
- Use a maintainer if the car sits for weeks.
Jump-starting (do it in this order):
- Open the trunk and expose the battery on the right side.
- Donor positive to the dead positive.
- Donor negative to a solid, unpainted chassis or engine ground on the Miata - not directly to the trunk battery's negative post. This keeps any spark away from the battery.
- Start the donor, then the Miata. Remove the clamps in reverse order.
Immobilizer (NB onward):
- The transponder in the key re-syncs on its own when power returns - a flat battery does not erase your key.
- If it cranks but will not start after losing power, cycle the ignition off and on and try again. A poorly cloned spare key is the usual culprit if it still refuses.
On every generation the battery is trunk-mounted, so keep a jump pack in the car - the trunk is exactly where you do not want to be fumbling on a cold night.