Too many variables to say. A contact on a door that gets used a lot doesn't last as long as one that's rarely used. Also the signal from one device can hop through other devices, which reduces the battery life of the device that is being hopped through, but a small system with few devices can also use batteries faster as the devices struggle to poll in to the receiver and try multiple times.
Its safest to use the correct mode for each device and change all batteries every year.