Some radios have a switch that selects high or low transmitter power. Always use the low power setting as much as possible to conserve your battery. Carrying an extra battery on a search mission is an absolute requirement. Rechargeable batteries lose capacity unless they are constantly trickle-charged. Because of this you may not know the capacity of a battery unless it has just been charged.
Alkaline batteries are the best to use as backup.
They are inexpensive, have good shelf life, and will last twice as long as rechargeable batteries. After you have used alkaline batteries on a mission they should be replaced with fresh ones. The used ones may be serviceable for non-critical household applications such as toys or portable broadcast receivers. For this reason, it's best for both stations to be as high above ground as possible. If the signal is weak it may be necessary for someone to climb a hill or a ridge or to stand on a nearby boulder to improve the signal strength.