Right folks ,first point is that this is not a Skoda, but a Renault Laguna, Diesel . It's my daughters ,and on cold days( no idea how cold ,she just says cold) it won't start . Typical female "won't start " - think she means it just grinds on till battery flat. SIL has charged battery ,and "tested" charging system using some gadget. He says his " gadget" points to alternator problems. I did a test on the system using a standard digital meter( All readings across the batery terminals). At rest , battery was about 12.5 volts. At switch on ,and system chek , this dropped to 12.2. At start this dropped momentarly to 12 v, rising to 14.5 once engine running, and revving, staying solid at this when back at idle.

My analysis of the battery- the low diferences would lead me to suspect that there is little problems ,as the voltage drop on high current output made little difference to the available voltage. Likewise the voltage on start was as expected. With problems on "on cold" starting ,I'd suspect glo plugs of givin problems .

Any ideas .

Standard problem on all cars is the electrical connections aren't clean and tight. Check earth straps.

On cold days it might be that she is trying to start the engine too quickly - is she waiting for the glowplug warning light to go out? Sometimes it is worth waiting a second or two after the warning light has gone out, especially on the coldest days.

After these it might be work checking whether the glowplugs are working properly -- not exactly sure how you do this but often some kind of resistance measurement.