One of the hardest things to estimate when speaking in terms of a trail camera is battery life. There are many variables that must be considered when trying to calculate the power consumption of your trail camera such as; the mode of operation being used, the number of pictures or videos taken, how many of the pictures or videos taken occur when the flash is needed as well as the temperature.
It is recommended that a good quality alkaline or lithium battery such as Browning brand, Duracell or Energizer be used. Using the recommended batteries will provide not only optimal performance of your trail camera but also provide the longest battery life possible.
A link is provided below to the Browning Trail Camera Power Pack which extends the amount of time your trail camera can be left in the field as it pertains to battery life.