When mine did this, it was terminal, the starter magnets had come loose, so it would start with a fresh battery, say once... then nada was pulling huge amps
When is the clock zeroing? When you try and start out? Filthy starter means does the clutch needs cleaning (the bendix) and the whole area between the starter motor and its shaft connection into the little gear box (this will become obvious when you get it apart!).
Exactly this time last year I had to get intimate with my starter motor on a trip, the grease plate had come off and welded itself to the windings, and like Welshman it was pulling huge amps and zeroing the clock instant I touched the starter. I blamed the battery at first but thanks this site I was pointed to the starter, which I took off and disassembled. I never did replace the grease plate... But in your case the magnets may also have taken leave and stuck themselves to the windings. You won't know until you take it off, which is a 10min job
I'd get that starter motor off and disassembled. Check out the stickies for this section, good write up on how to do (it's straight forward, I only read it after doing mine!). Perhaps also do a search on starter motor + grease plate.
Will do but is it still likely to be starter as its seems to be as the key is turned off and on? or are there any other posilbilities for the discharge..?
Apologies, I thought the clock was zeroing when you pressed the starter button...not just when you switched on. If that's what happening then surely something is shorting?