I realise the obvious answer is a flat battery, but why a rapid ticking ? In the movies when a car won't start due to a flat battery you hear it chug, not tick. Today was the 2nd time in 2 months I have had to re-charge my battery. Both times when I hadn't used the car in approx 12 days. It seems if I use the car at least once a week it is fine, but stray too far beyond that and it goes flat. Does this definitely sound like a flat battery or could my battery charger be fixing another issue ? As a new battery is £140 so I want to make sure it is definitely the battery at fault and not some kind of immobilizer. The voltage was around 11v when I started charging the battery.

I have a MK3 Mondeo.

 

 

That can happen when the battery is so low the additional load on it when the starter solenoid engages causes the voltage to drop enough so the solenoid instantly drops out again.

As the battery recovers slightly , it pulls back in and the cycle repeats.

The battery is likely on the way out. Normal car batteries cannot stand being completely flattened more than a very few times before they lose capacity and pretty much just stop working.

I find the last about 3 - 5 years, as long as they are not allowed to go flat.

 

Where are you buying the battery from - Euro Car Parts and Car Parts For Less (same company) are a rip of lately on some stuff. Want over £400 for a battery for my 320 2 litre petrol BMW - dealer fitted price £300 - Halfords same spec battery £185

CTEK MX5 Battery charger - £135 at ECP - £79 at Halfords. Original selling price at most places before Covid was £69