It is useful to estimate the remaining capacity of the Oyster Cellular batteries. The nature of the Lithium AA batteries (LiFeS2) recommend for the Oyster requires a capacity estimate to be made based on sampling the battery voltage after at least 3 hours at a low current. The Oyster attempts to sample the battery voltage at a low current, and the highest recent sample is stored in Analogue 1. This can be used to make some rough estimations of the remaining capacity.


Voltage Range
Capacity Estimate
V Batt Good Status Flag
4.80 – 5.30 V
40% + remaining
Set (1)
4.65 – 4.80 V
25 – 40 % remaining
Set (1)
4.50 – 4.65 V
10 – 25% remaining
Clear (0)
4.20 – 4.50 V
0 – 10% remaining
Clear (0)


Note:

  • This applies to firmware version 1.1 onwards
  • This applies to Oyster Cellular devices only.
  • These groups do not imply a linear relationship in each range. The voltage should simply describe the 4 groups.
  • More accurate estimations are not possible at this stage because of the battery chemistry.
  • This will be less accurate if the device does not regularly sleep for 3 hours. For example, hourly heartbeats may not allow the battery voltage to recover completely, leading to a lower estimate.
  • Further to the previous point, the voltage will not recover completely if the device is usually colder than 5 degrees C. The low temperature stops the battery voltage from recovering completely, providing a lower capacity estimate.


Analogue 5 (Loaded Voltage) is an instantaneous sample of the battery voltage, and varies considerably with device activity. This is not useful for battery capacity estimates.