Typical OEM vehicle batteries are usually not the highest grade available and in my own auto ownership experiences 4 or 5 years seems to be the longest an original battery will last before it shows signs of deterioration. Since you don't mention the vehicle age I will presume it is the last model year for the RX-8, which was 2012. At five years old I would definitely suspect the battery is due for replacement. If it is an older model year, then absolutely the battery could be all done.... view full answer...