Campbell Scientific Wireless Sensor Network (CWB100, CWS220, and CWS900) - Manual (Page 65)

Appendix C. Battery Life
C.1 Battery Characteristics
The battery life of the CWS wireless sensors is a function of the polling
interval, repeater usage, type of batteries, and temperature. The types of
batteries that can be used in the sensors are AA sized alkaline, Lithium, NiMH,
or NiCd; their capacities and characteristics are:
Battery Type
Manufacturer Capacity
mWH) Temperature
Characteristics
Alkaline Duracell MX1500 3800 -20 °C to +54 °C
Alkaline Energizer EN91 3800 -18 °C to +55 °C
Lithium Energizer L91 4000 -40 °C to +60 °C
NiMH Duracell DX1500 2500 -20 °C to +50 °C
NiMH Rayovac LD715 2500 -10 °C to +45 °C
The capacities that are listed are for 21° C operation; for all the battery types
(except Lithium), the capacity decreases as the temperature decreases. For
example, the capacity of the Alkaline batteries decreases by 30% when the
temperature is at 0° C. All these batteries can be used below the stated
temperature range (the Duracell Alkaline and NiMH have both been tested to
-30° C), but their capacity is reduced.
For the rechargeable batteries, while all types can be used, by far the best type
to use is the “low self-discharge” NiMH batteries. Both of the NiMH batteries
listed above are of this type. The normal NiMH and NiCd batteries have very
high self-discharge, and would probably only last for a couple of months.
C.2 Effect of Polling Interval and Repeaters on
Battery Life
The largest factor affecting battery life is polling interval, followed by repeater
usage. This is because the radio RX/TX current is the dominant drain on the
batteries. Any sensor that is used as a repeater by another sensor will also have
its battery life decreased, as it has to send its own data as well as data from
sensors repeating through it.
Using the Duracell MX1500 Alkaline batteries, derated by ~20%, gives the
following expected sensor battery life:
C-1