The Oyster3 has in-built battery monitoring capabilities. It is critical to any application that:

1. The batteries last long enough so that frequent changes are not necessary
2. Low battery alerts are sent in a timely manner - so that battery changes can be made before batteries run flat. 

The Oyster3 should be used with either of the below battery types

• Lithium Iron Disulphide (LiFeS2)
• Lithium Thionyl Chloride (LTC)
• Alkalines (can be used but not reccomended)

See Battery Recommendations [Oyster3] for detail on selecting the right batteries.

The differences in battery chemistry mean the battery monitoring approach is slightly different for each type. 

However, the firmware takes care of all of this for us, across all DM device types, and simply sets flags in the payload which we can alert on.

Setting up Low Battery Alerts

Information about editing parameters is available → OEM Server - Getting Started

The below are already configured by default - so we don't need to go make any changes, or configure anything unless we have special requirements.

Battery Good + Battery Critical Flags

The device keeps two battery 'flags':

Battery Good Digital Input 

• Mapped to Digital Input 1 by default.
• Also appears as Bit 1 in the Device Status Flags 
• Active '1' when the voltage is above the Battery Low Threshold - and inactive '0' when below this threshold.

Battery Low Threshold

If Battery Chemistry is set to AutoDetect and the Battery Low Threshold parameter set to 0, on startup, the device records the initial battery voltage, and works out if LTC, LiFeS2 or Alkaline batteries have been inserted. 

Then, the battery low thresholds for each battery chemistry are as follows:

• LTC - 7V loaded voltage (analogue 5)
• LiFeS2 - 4.85V
• Alkaline - 3.6V

The battery voltage reported in Analogue 1,  is reported as the maximum voltage seen over a 3 day period. 

This is because battery voltages do bounce around somewhat and this provides some averaging. Additionally the different chemistries have different discharge profiles which require different measurement methods.

We can adjust the thresholds if desired by changing the Battery Chemistry dropdown and setting a value in mV for the Battery Low Threshold. This is typically not required, only change if you know what you are doing. 

Battery Critical Digital Input

• Mapped to Digital Input 2 by default
• Also appears as Bit 5 in the Device Status Flags
• Active '1' if a brownout occurs. 
  • On the Oyster3 - this is if the voltage ever dips below 3V - which is too low to properly power the device. If this occurs - it is because the batteries are on their last legs, and need to be replaced immediately! The device needs at least 3V to operate.

The above flags mean we have 3 distinct states