The internal batteries for the timer are "nc-aa660ft"
seen these batteries ? I think most if not any 1,2V AA cell will do the Job
http://www.ebay.de/itm/Batterie-Telephone-sans-fil-pour-SONY-MZ-R5ST-/351516807256?hash=item51d808d058:g:pEYAAOSwPgxVSFGM
I´ll check my unit later.probably my batteries are drained out too.
But as i never used the timer function it didn´t happened to cause any problems.