In order to maximize battery life, our recorders go to sleep after each recording period and wake up some time (30 seconds for terrestrial units, 3.5 minutes for marine units) prior to the next recording period in order to prepare for recording. Additionally, our recorders will not sleep for periods of 30 seconds or less.
It is important to keep this in mind when scheduling on/off recording cycles. The more on cycles the recorder has in a given day, the more times it will have to wake up prior to recording, adding additional "active" time that drains the batteries more than sleep does. It is possible to schedule recordings in such a way that the recorder does not sleep at all, even when not recording.
For example, an SM3M unit with a 2 minutes on/4 minutes off duty cycle will never go to sleep. Marine units must wake up 3 minutes and 30 seconds prior to the next recording period in order to "warm up" their hydrophones, and the recorder will not bother falling asleep for 30 seconds or less. To keep the same ratio of recorded time to unrecorded time while improving battery life, use a longer cycle, such as 10 minutes on/20 minutes off.