mx5cartalk.com

Don't get a wet-cell battery, just a dry cell type.
Wet cells can cause problems later on down the track, like rust.
If you've managed to get 7 years out of the standard battery, why would you want to use anything else?

The Panasonic batteries are good, as are the Yasue(?) and most other japanese brands.

Mania have some at resonable prices, but you can also search around at Battery World and other retailers.

The NRMA do not carry batteries for NA or NB's.

Supercharge make a battery to fit the MX5. A few guys on the forum are using them. They are a calcium battery so vent less than a normal battery and cost per performance is very reasonable. American Autoparts at Homebush/Beverly Hills are selling them for under $80. My battery is finding it hard going on these cold mornings too so I think I might be needing a new one soon, though when the warmer weather comes back it tends to recover somewhat.

For more info try doing a forum search. There is quite a lengthy discussion about batteries in one of the topics.

oops