The SM3 and SM4 configurators can estimate how long your recorder will last based on your settings and schedule, as well as the energy capacity of the batteries you will be using. Under "Deployment Scenario," you can enter the energy capacity of the power source you will be using to get a rough idea of when the recorder will run out of battery.
To calculate the energy capacity in Watt-hours, you need to know the battery's voltage, measured in Volts, and its charge capacity, measured in amp-hours or milliamp-hours (1000 mAh = 1 Ah). These figures can typically found on any battery's data sheet. Note that charge capacity typically decreases as more power is drawn from them. The typical power draw level for your recorder can be found in its user guide.
If we are powering an SM4 using an external golf cart battery that has a voltage of 6 V and a charge capacity of 215 Ah when enough power is drawn from it to completely discharge it in 20 hours. The SM4 uses much less power than that, so the figure of 215 amp-hours should be a safe, rough estimate. Therefore, our estimated energy capacity would be 6 V x 215 Ah = 1290 Wh.