tested the voltage at idle reads 14.25 volts could this mean the battery is being overcharged
also the volt meter on the dash panel reads around the same could thie be the cause of my
battery ging flat

not real sure bout au's but im pretty sure my elxr8 charges at about 14 volts at idle (from memory), well untill the thermos turn on then it drops a bit but that is due to the underdrive pulley set im running.

how often does the battery go flat?
have you load tested the battery?

battery could have a dead cell?

14.25 volts at idle is ok.
Does the battery need fluid?

Most voltage regulators are at or over 14V so that's perfectly normal. You need more than 12V to charge a battery.
What are the conditions of your battery going flat?