I've got a MK1 Focus Diesel and just lately it's been difficult to start. I commute about 40 miles a day and don't use it for short journeys so it should have ample time to charge the battery.

I replaced the battery and alternator about 18 months ago but it's showing all the symptoms of a battery that won't hold enough charge.

For instance I parked up last night after a 40 mile journey. This morning it turned over ok but didn't catch. I tried again and there wasn't enough charge left to crank it sufficiently.

I took it to Halfords last week and the lad put his battery tester on it and told me it had "60% starting capacity", whatever that means, and that "it should be fine".

So how reliable is the test that Halfords do and can a battery die in 18 months. It's a Bosch so it's not a cheapo one.