05-06-16, 09:07 PM
It could be the battery, but even with a duff battery the voltage should be higher at 5k rpm. An alarm could possibly flatten the battery in 4 weeks, especially if its a bit "tired". Both rectifier/regulator or an alternator fault are a possible cause. Its possible for the alternator to have shorted turns or some coils to be open circuit and still give some reduced output, so the 12.5v @ 5k rpm unfortunately doesn't completely rule out a faulty alternator. If you have a multimeter you can do some basic resistance checks on the alternator windings while you are waiting for your new battery. On the thou (gen 1) behind the LHS side panel there's a connector with 3 white wires. With this disconnected measure resistance on the alternator side between each of the white wires. Should be around 0.3 Ohms. There should be no connection (high resistance) between any of three wires and ground.