The Tempest device uses an integrated solar power module with vertically oriented solar panels that are ideal for low sun angles at high latitude locations.
Internal Rechargeable Battery
The Tempest device uses an advanced rechargeable battery that is well suited for use outdoors and in cold temperatures. LTO batteries are safe on the environment and have a very long lifetime of almost 50,000 cycles - which is decades of recharging. If the battery capacity in your Tempest gets too low, software will automatically put the device in a power saving mode.
The device must be powered on in order for battery charging to occur. When the voltage drops to around 2.4 V the solar panels will start charging the battery. It will charge faster if it gets direct sun but can still charge slowly with indirect sunlight. The battery will stop charging around 2.6-2.8 and then decrease to a safe operating voltage around 2.55v.
Battery Level Indicator
You can check the battery level for your device by viewing the status page for your station: In the app, go to Settings > Stations > (choose a station) > Status
Battery Card Display
You can display a device's battery voltage in the app. To enable a battery card indicator on the data display, go to Settings > Stations > (choose a station) > Advanced > toggle Enable Battery Card