One problem related to battery dead has been reported for the 2004 Mazda RX8. The most recently reported issues are listed below.
If the car stalls after a cold start, it is either very difficult or impossible to restart. Using the procedure in the owners manual for this situation will work, if the battery does not fail first. I have had this happen twice, once the car was towed. The second time, the battery died while attempting a restart per the owners manual, but the car was in the garage and I recharged the battery and eventually got the car started.