Tempest Battery Voltage Range

What is the nominal voltage of the battery in the tempest ? At what voltage dose it drop into power save mode ? Thanks.

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Hello chris4

there is not just one voltage, there are several levels. Here is the complete list

Power Modes

Mode 0

Voltage >= 2.455

Full power all sensors enabled

Mode 1

Voltage <= 2.415 or >= 2.41 from Mode 2

Rapid sample interval set to six seconds

Mode 2

Voltage <= 2.39 or >= 2.375 from Mode 3

Rapid sample interval set to one minute

Mode 3

Voltage <= 2.355

Rapid sample interval set to five minutes

Sensor sample interval set to five minutes

Lightning sensor disabled

Haptic sensor disabled


@eric is there a voltage which triggers the solar panels to activate? I ask because my tempest has been setup outside for 3 days now. When it was first installed the voltage was at 2.60, and its gone down steadily to its current voltage of 2.48. For 2 of the 3 days we’ve had plenty of sunshine, yet I haven’t seen the voltage increase at all. Thanks!


I have seen exactly the same thing on my new unit. It varied from 2.57 at first turn on down to the current 2.49 with the status always reflected as “good”. Just curious as to what I should expect.

Same here, it started at 2.58 and is now down to 2.48 after 4 days. It always drops, never rises. Not what I expected from a solar charger. Would love to know what is expected.

This is normal behavior. Apparently, it will charge when it drops below a certain voltage threshold.


My battery hit 2.45v today for several hours and now appears to be charging, back up to 2.5v and climbing.

Same here. Tempest hit 2.45V and it spent today charging back up to 2.55V.

My Tempest has been below 2.45 for a couple of days and has not started charging yet.

That’s strange. Mine dipped below 2.45V again today and then charged back up to 2.53V.

The type of battery in the Tempest is a Lithium Titanate or LTO. While I don’t know the specifics of our batteries, in general 2.40v is nominal and it has a range of 1.80v to 2.85v. So it seems that the battery will hover just slightly above nominal for as long the station is operating.

Seems like a great pick for a battery type. Here is the description from Battery University:

Long life, fast charge, wide temperature range but low specific energy and expensive. Among safest Li-ion batteries.



Thanks for the data. I just got my Tempest online today and was wondering how the battery would perform and how charging would work, especially during the winter season.

My Tempest has been bouncing between 2.39 and 2.40 for almost 18 hours. It’s installed in a location that gets several hours of direct sunlight each day.

just checked and it is slowly charging according solar radiation (at 2,44 now)

Eric - Thank you. Is this normal operation for charging?

I received my Tempest on June 17th. When I installed it, the voltage started at ~2.50 and has dropped consistently since then bottoming out between 2.39 and 2.40. When will the solar panels kick in and start charging the battery? It’s been stuck at 2.40 for the past 18 hours with plenty of directly sunlight.

It’s normal. See here…


What is your station ID? It should have started charging at about 2.45V. My field test unit charges about every three days.

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My Station ID is 2474.

I can’t compare with my test version but we see often in the beginning a large discharge followed by several small charges and the gradually it goes to nominal. Not sure it is chemistry or regulator but it’s like breaking in. Just follow it for the coming days and if you have several sunny days it should slowly go over 2.5 easily … also don’t expect it to go up and down like the Sky units. Other type of battery with really different behaviour.