Campbell Scientific CSM1 Card Storage Module - Manual (Page 25)

C-1
Appendix C. Card Batteries
The make and type of battery supplied with the memory card can vary with the size and
manufacturer of the card. Campbell Scientific reserves the right to supply cards of
different manufacture with different battery sizes and types.
The batteries fitted to the cards are readily obtainable from electrical suppliers. You must
ensure that the replacement battery is compatible with those recommended by the
manufacturer of the card. Please refer to the manufacturer's instructions for further
details on removing and replacing the batteries.
C.1 General
There are two technologies used in the batteries, both of which are lithium
based:
a) Lithium polycarbonmonofluoride (Lithium CFX), which is the newer
technology. These batteries are rated to very low temperatures, e.g. -40°C,
and usually have a slightly higher initial capacity than those below.
Manufacturers' part numbers for these batteries normally start with a 'BR'
suffix.
b) Lithium manganese batteries, which are currently more readily available.
These batteries operate at temperatures down to
-20°C. The suffix for these batteries is generally 'CR'.
For some battery sizes either type of technology is available. It is important to
match the digits after the suffix, e.g. BR2032 is equivalent to CR2032.
Both battery types have reduced capacity at low temperatures, e.g. at -20°C the
capacity may only be 50% of that at room temperature. However, this is not as
critical as one might imagine, for the following reasons:
a) Power is only taken from the back-up battery when the card is not
powered from the CSM1. Therefore if the card is plugged into a CSM1
that is plugged into a datalogger, the back-up battery is not in use.
b) Power consumption from the back-up battery is highly dependent on
temperature. For example, typical figures for a 1Mb card are 0.7mA at -
30°C, 2mA at 25°C and 16mA at 60°C. Therefore, the reduced capacity is
offset by the lower power consumption.
c) Although the effective capacity of a battery is reduced at sub-zero
temperatures, if the card warms up, the effective capacity increases again.