There was a problem with the dials on pre 2003 Focuses which sounds like the problem you have. Ford originally charged £600 to replace it but after a campaign on watchdog it went down to £99. Phone your local Ford garage and ask them about it.

If the battery and/or alternator were the problem then the dials would do 'a sweep' just after you turn the key.

If it were the VSS then just the speedo would be playing up, not all the dials.