I too have an '03, but unlike your's, mine doesn't have P/door locks or alarm. But! just like yours, mine does have the factory warranty that is still in effect. To keep the warranty effective, I am taking mine to an authorized dealership to have it serviced at the appropriate intervals. Mine is about due for it's 30,000 mile tune-up at which time they will replace the plugs and wires as well as the filters (fuel & air). If you want to know how to get to the plugs and wires, ask your Mazda Mechanic to show you. Devolope a rapport with your mechanic. He will be a good friend to have in times of need. The dealership that sold me my '03 just started their franchise so I'm going another dealership a bit out of my way to have the servicing done by a seasoned Mazda mech.
As for the battery, they are a sealed unit that needs very little to no servicing and having them in the trunk on the passenger side transfers some weight to the rear of the car keeping it at the ideal 50/50 weight distribution.
I just got mine on the 28th of June. After driving Opel GT's for the last 20 or so years, I find it a nice refreshing change. It gets better milage, it's quite a bit quicker, handles better and best of all, it is a convertable!
It may be a while though before I change my address to " snipped-for-privacy@comcast.net".
Todd Benson snipped-for-privacy@comcast.net