I'm pretty sure this is either a battery Ampage/voltage output issue or the variation on the starter click.
1st check the voltage of the battery using a volt meter. Need to check you get 12.5 Volts unloaded.. ie no starter. (good condition battery) If Below 12v unloaded then suspect duff battery.
If you have over 12 Volts unloaded and If you get under 9 Volts loaded ie starter button engaged (you may see as low as 6 Volts) then it's the battery...
If you get over 12.5 volts unloaded and still over 10 when loaded then it's the starter.
I have had this before on my original Aero. P.S. only get BOSH starter as variation in quality can cause repeat symptoms quickly without seemingly at fault!!
BOSH btw.. should not be overly expensive.