Nothing, the red warning light is supposed to flash when the car is immobilised, it's an anti theft deterrent.
3 days is a bit weak for a battery to hold charge, 2 weeks is not uncommon so your battery may be tired. Is anything else on? Radio, or SatNav left connected?
The cars really are best left on a battery conditioner, something like an Optimate or Ctek both are popular and simply plug in to the cigarette lighter in your glovebox, assuming your garage has mains electricity of course.
Both are 'float' chargers and so can be left connected for long periods of time.
All the best and welcome.
Colin (2008 +4 Duratec)
