The batteries in your avalanche transceiver will typically last 200 to 300 hours depending on the type of transceiver you own and how much searching you do. At a minimum, an avalanche transceiver with fresh batteries must be able to transmit for 200 hours at 10°C (50°F) and then receive a signal for at least one hour at -10°C (14°F).
Install new, high quality, alkaline batteries at the beginning of each season. All of the batteries should be replaced at the same time using same brand. Never use rechargeable batteries.
Replace the batteries when they get low based on the manufacture's recommendations. When in doubt, replace them when they reach 50% of capacity. Batteries are inexpensive—don't be a cheapskate at your partner's expense!
You should remove the batteries from your avalanche transceiver at the end of each season to prevent damage due to battery leakage (battery leakage will void most manufacture's warranties). According to Mammut, you should return your transceiver to the manufacture and have the terminal contacts replaced if you see any corrosion on the terminals.
Digital transceivers display the strength of the batteries on the screen. Here are a few manufacture's statements regarding their battery indicators:
The transceiver comparison table displays the manufacture's stated battery life. For example, when the table lists "250/15", it means that the manufacture states that the transceiver can receive for at least 250 hours (presumably at 10°C) or receive for 15 hours (presumably at -10°C).
Beginning with version 3.2, the Mammut Pulse can accept either alkaline or lithium batteries. Lithium batteries are lighter, last longer (according to Mammut, in normal conditions the batteries will last 50% longer than with alkaline), don't corrode, and are more expensive. Note that you must change an internal setting in the Pulse before changing the battery type. And never use lithium batteries in avalanche transceivers unless the manufacture clearly states that they are supported.