NB: Lithium AA batteries are strongly recommended over alkaline batteries
The Oyster uses 3 x AA 1.5V batteries.
The cellular modem on the Oyster draws large peak currents when transmitting, and the modem requires a certain minimum voltage to operate. Because of this we highly recommend the use of "off-the-shelf" Lithium batteries available at your local retail or hardware outlet, as they can maintain their voltage across their useful life and can deliver good peak currents. These batteries generally use a LiFeS2 chemistry.
The Oyster Cellular will work with alkaline batteries, but they will not work for as long. The voltage drop on the regular discharge curve of alkaline batteries will result in about 40% of the capacity unused.
The Lithium batteries have the added advantage of being higher capacity, and can operate better in extreme temperatures.
Duracell Ultra Lithium
NOTE: The Oyster does not support higher voltage 3.6V Lithium Thinyl Chloride batteries - do not use these as they will damage the regulator in the Oyster!
See attached for Oyster Cellular Battery Recommendations document