AU Battery Light comes on and off randomly

[macca1810]

Hey
My au has for the last month been having the battery warning light on the dash come on and then always go back of within a minute. Had no problems for 3 weeks but then got a dead battery out of the blue. Charged the battery to full and it didn't hold but that's understandable considering its over 3 years old so replaced it thinking this would stop the warning light coming on but no such luck. Just wondering where my first port of call would be? Is this a common easily fixed problem? I hope so because i am busy as hell every day 12 hours for next month more or less seeding so don't have time to worry but i'm just hoping it won't wreck my new $105 battery. Hope someone can shed some light thanks in advance