kenwood dcs-8200 clock issues

[m3vuv]

hi all ive just got the above scope,when i got it the display said low batt,after stripping it down i found a tabbed lithium button cell soldered to a pcb,i didnt have a replacement so got 2x aaa nickel metal hydeide cells in a holder in series,so 2.4v as opposed to 3v,the leads from this are soldered where the original battery was,it no longer says low batt but the clock doesent keep the time date etc when the scope is power cycled,its not an issue as the scope still works fine,any ideas if 2.4v and not 3 will cause this?,cheers in advance,73 m3vuv.