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Appendix A – Battery life calculation
When to replace the batteries
Compared to the cost of deployment, the cost of a new set of batteries is close to
negligible. We highly recommend that the batteries be replaced before every
deployment unless there is no doubt that they have sufficient capacity.
Battery voltage does not decrease linearly and is therefore not an accurate
indicator of battery capacity. However, if the logger software indicates that the
batteries have less than 12V remaining (6V for single channel loggers), the
batteries should be replaced.
Predicting battery life
Battery life prediction is a complicated issue. In RBR loggers, battery life is a
strong function of the type of logger, the type and number of sensors attached,
the sampling scheme (sampling period and the use of: thresholding, real-time
data collection and averaging), and the temperature of the water during the
deployment. Manufacturers’ data for the batteries do not provide information that
can be directly related to way the batteries are used in RBR Loggers.
The RBR Windows Software calculates the expected battery usage (in mA Hours
- mAH) for the logger during setup, see page 15. The nominal capacity of the
batteries is 1300mAH at room temperature. The software will warn the user if the
expected battery usage for a particular deployment scenario is above 1000mAH.
The software will not prevent a logger from being started even if a warning is
given. In tests at RBR Ltd. of multiple examples of various brands of batteries at
6°C, all examples were able to provide the threshold capacity of 1000mAH. The
user should view these predictions and further de-rate the batteries if the
expected deployment is in cold water. The battery usage estimate is stored as
part of the log files (page 21) and may be used after deployment to enable the
user to obtain a characterization of how a particular logger performs.
RBR continues to characterize battery life in its loggers and will continue to
improve the battery life calculator in future versions of the RBR Windows
Software.
Battery life will be reduced if the RS485 serial transmission protocol is employed.
The consumption for the RS485 driver is defined as 2.5mA nominal. Hence for
every hour of deployment, 2.5mAH must be added to the battery drain figures.
When in doubt, replace the batteries.
