Small battery life (XBee S2CTH)

I’m having problems with the life duration of batteries in the Digi Xbee s2cTH nodes of my project (firmware 4060).
Basically I’m using several nodes to measure the temperature in different places inside of a room, to do it I’m using thermistors.
The mode of operation is that nodes are sleeping cicles of 28secs, although on the other hand the collector asks nodes every 60secs about their inputs value.
The life time of the batteries (9v -200mah) is about 100hours (if batteries are cheap the duration is reduced to 40hours), at the begining my main suspects were these thermistors due to they were always consuming (independently if the node is in sleep mode or not).
For this reason, I’ve done several test in whom I’ve removed all electronic components, except a small capacitor, a voltage regulator and the node xbee. So basically I’ve reduced the elements to the minimum needed and now the node is sending the (%V) parameter instead of the temperature, all the inputs/outps are put to down, the pull up resistors are disabled and so on… But surprise! The life time duration of the batteries is exactly the same.
May some body give a clue were could be the problem? Why is the lifetime of batteries so small?

SP=AF0 (28sec)
ST=3E8 (1sec)

Thanks for your help