My battery is fine but my 1.8 diesal ford focus won't start every time any idea?

My battery is fine but my 1.8 diesal ford focus won't start every time any idea?

You expect us to diagnose a non start with zero info? Is the starter turning, is it trying to fire?

How do you know for a fact the battery's OK, and don't say 'because the lights/stereo work.'

If the battery really IS good and the starter just churns away at it have you checked the glow plugs?

Poor earth. IF the battery IS good

If it misfires on starting the glow plugs are suspect.

Renew your glow plugs.