Sky battery life



My Sky went off-line yesterday.
Battery voltage dropped from 2.85 V to 1.81 V in about 90 minutes.
Sky uptime was 234 days 7 hours 39 minutes 51 seconds.
Sky had been installed 7 months and 3 weeks ago, around June 20th 2018.

Batteries were those recommended by WF.


Ignoring the seemingly reflex responses of ‘batteries do not like cold’ and ‘do you have a bad cell’ and the ‘they fall off a cliff fast’ we always get to such reports, does @WFsupport or @WFstaff have a particular voltage threshold that we should be concerned to see for Air or Sky ?

For a working system with good batteries in it of the recommended type, what’s the battery status voltage where we need to cut our Amazon orders for more batteries ?

Is it 3.20 V ? 3.10 V ? 3.00 V ? Something else ? Or are we just going to wake up one cold morning and find everything offline when they fall off that cliff ?

Looking for ‘WF’ answers only here please…


Speaking of Sky battery requirements; The wind in the Sky seems to fail at just below 2.629 vdc yet the web application does not give a notice to replace the cells until it is below 2.2 vdc.

It has also been demonstrated that the cells are failing rather quickly once they reach 2.7 vdc.

@dsj Will you please comment on this?


Hi @GaryFunk,
Sky works fine down to 2.2 volts in

  1. my above zero temperature
  2. With the Australian frequency
  3. With Alkaline batteries
  4. Non power save mode

I wonder why the voltage sometimes dips for a couple of minutes? I wonder if there is a larger than usual current draw from the battery?
If a lithium battery is near its cliff and then a larger current is drawn it might cause a steeper cliff.
My voltage graph did show a drop for an unknown reason then recovered here:

If that voltage drop is actually a real momentary very high current draw that would cause a steep cliff?
I dont expect it was actually a short because I would have expected a more gradual rise to its normal voltage. But perhaps the ‘short’ was very short at only the moment the voltage reading was being taken which then gave 59 seconds for it to recover?
I realise this is unlikely, but when I brainstorm it is important to offer all ‘thoughts’ to help inspire the solution.
cheers Ian :slight_smile:


David has stated that the voltage is measured every 10 minutes. That explains the 10 minute gap. My guess, there is a timing issue when the measurement is called for and the system returns the value to slowly.

This is one of those ‘features’ I have learned to live with.

It’s interesting that you are on Alkaline cells and the Sky preforms well at a lower voltage. @eric is on the Lithium cells and the (beta) Sky wind sensor went into failure between 2.629 and 2.620 volts. Being a beta unit may be the reason.

Others have seen complete failure when the Lithium cells hit 3.0 volts.

Is any one else << pick your adjective >>?


I replaced the Ultimate Lithiums when I had a low battery alarm/shutdown in December with standard Eneloops for a test and as I had no spare Ultimates. My SKY varies from maybe 2.48V to 2.5V -depending on temperature of course and it is quite happy, no dropouts and batteries have been in pretty close to 8 weeks now. As the PV option is being tested, I am happy to use the Eneloops until that is available (With a set of Eneloop pros on standby just in case :slight_smile: )


I put in cheapo alkaline cells from a discount supermarket (€1.80 for 10) about 140 days ago. AIR is reading 2.96 today and SKY 2.67, everything working fine (well, almost, but nothing to do with the batteries!). Being of Scottish origin, I said to myself, ‘Why pay the earth for top-grade batteries?’

The outside temperature range the units have felt was ~37°C to ~3°C, but I imagine the batteries may have felt a somewhat smaller range (plastic casing altering the inside temperature and the thermal inertia of the battery mass).


All sensors in SKY should work down to about 2.0 V.

We have not observed this. The sonic anemometer itself should actually work down to about 1.0V, though other parts of the SKY will stop working well above that threshold.

Yes, that’s consistent with what we’ve seen. We’ll raise the “replace” threshold from 2.2V to 2.7V in future releases of the apps.


Take a look at the station @eric has up. It failed.


remember those are rechargeable NiMH and not Li (didn’t have on stock since the previous set dropped in no time as usual) Wanted to test those for a change and see how they behave …

wind and UV/brightnes failed jan 27th and see battery levels before and after didn’t change drastically (except a dip by freezing weather)


As the Eneloops function perfectly at 2.5V (in above freezing temperatures) will that mean the SKY shuts down at 2.7V or we just get a warning?
Actually-how about a switchable threshold, default 2.7V for Ultimate Lithium users and 2.2V for Li-Ion , that way everybody is covered :slight_smile:


It would just be a warning. But yes, this simple change would mean the warning would only be accurate(-ish) for the Ultimate Lithiums. A configurable warning is something we could add later.


As long as it is just a warning, all good, I was a little concerned it would be a shutdown as well. Thanks David.


That is not the issue. The Sky shows a wind sensor failure at 2.62x vdc while others sensors functioned

@dsj can you explain this failure?


I’ll let this as is for now, but will try to change them next week end again for the usual ‘good’ batteries. First get a set of these again. And hope it doesn’t rain coming week end.


Is it possible to have two different warnings: one to say time to get replacement batteries ordered; and a second one to say batteries need to be replaced? Use 2.7v for the first warning; & 2.2v for tge second. here’s how my set failed:



In your case that still would not work for most. It looks like once your voltage hit 2.7 your unit died in less than 48 hours. Not enough time for most users to order and receive new cells.


Yeah, that’s a good point. BTW, temps were pretty mild (for Winter) at the time: 35°F.-42°F. But if this was Summer time, I wonder if I’d have eked out a few more months?


With the long shelf life of these batteries, why not simply have an extra set on hand so that when the ‘unexpected’ occurs, you simply grab your extra replacement batteries?