Digital Matter Support

Battery Capacity Estimate & Low Battery Flag

Predicting the battery life of Lithium batteries is quite difficult due to their chemistry. The batteries will output a constant voltage until nearly the end of their life, and suddenly this drops off. Meaning early warning, and accurate gauging of battery life is quite difficult based on voltage alone. 


The Oyster2, Falcon and Remora2 are fitted with a coulomb counter, which tracks energy (in mAh), used by the battery. 


This can be used to estimate the battery percentage, and remaining battery life. However these estimates rely on an assumption of the total capacity of the batteries. This can vary per battery type, and even on a single type quite significantly due to temperature variations. 


Oyster2 and Falcon


The device 'guesses' as to whether the installed batteries are Lithium Iron Disulphide (LiFeSO2), or Lithium Thionyl Chloride (LTC) based upon the battery voltage reading. LiFeSO2 are 1.5V nominal per cell compared to LTC 3.7V


i.e. 3 x 1.5 LiFeSO2 batteries will result in around 5.2V total supply voltage when fresh. The LTCs will read around 12V.


Once this is determined the following assumptions are made:


LTC - capacity of 1650mAh

LiFESO2 - capacity of 3100mAh (Energizer Ultimate Lithiums are assumed)


Remora2


14Ah capacity of the 2 x D Cell LTC batteries is assumed.


Given knowledge of the battery capacity, the remaining battery % can be calculated. 

The mAh usage is counted from start up, so while the coulomb counter is far better at measuring the battery level than voltage alone, it is not infallible.


The percentage (reported in analogue 6) will and mAh used by the device (reported in the device statistics) will reset on a hard reset. This in most cases will line up with a battery change so works well.


The assumptions can be changed under this parameter tab in System Parameters if required.



Low Battery Flag and Alerts for Low Battery

Our devices devices use a 'Battery Good' Flag. It is set '1' when the battery is 'good', and cleared '0' when the battery is not good. This applies to both battery powered devices, and the internal back up battery of powered devices. 


Check the 'DM Data Fields' integration document section on the Digital Input field to see where it is displayed in the status flags if you are using your own platform.


For older firmware it is set when the battery percentage is above 15%, and cleared when below this. this was changed as below:

DeviceFirmware changed to 20%
Oyster22.4
Falcon2.4
Remora2unchanged


This is when the standard "Low Battery Alert" in Telematics Guru will fire. 


The Battery Percentage is also reported in Analogue Input 6, and is very useful for setting alerts as they can be set at any level and not just the pre-defined 'battery good flag' level. 


This is where the percentage should be read from in a 3rd party platform.


            

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