On Fri, 03 Aug 2007 01:34:59 -0700, wrote:

And what happens with a mobile ticket if your battery goes flat ?

Chiltern have an FAQ page for their mobile phone ticketing:
http://www.chilternrailways.co.uk/content.php?nID=165

"Q: What happens if my mobile battery goes flat before or during my
journey – or I forget / lose my phone?
A: Your mobile phone will be your 'ticket' so it is your
responsibility to look after it and have enough battery life for your
entire journey. However, our scanners will have a record of who is
expected on any particular train, so it's wise to carry additional ID
as back up.

Q: Do I need proof of identity (as well as my mobile) to get through
the barriers?
A: No. However, if you are unable to produce the correct barcode on
your phone, you may be allowed to pass if you are able to produce
additional ID."