Tempest Battery Charging Max Voltage?

I hear that some are getting 2.7 - 2.8 volts when their Tempest is fully charged. Mine will only get to 2.6 max…most of the time my max is 2.57. Why is it that I cannot get above 2.6 on a full charge? I have PLENTY of sunlight…and no obstructions. Reason why I am asking is that if the weather goes bad, for 4-6+ days, my tempest battery gets low. If I had 2.7+ volts, I could get a few additional days to push beyond the multi-day rain/snow days. Any and all help is greatly appreciated…

I have a 1 month old unit located in Northern New Jersey.

My unit peaks at 2.81v but drops very quickly to around 2.7v and then a much slower drop from there. As an example, the last 2 days shows 2.81v at 10am, 2.81v at 1pm, 2.73v at 4pm, 2.67v at 7pm, 2.65v at 10pm, 2.64v at 1am, 2.63v at 4am, 2.62v at 7am and then it quickly starts charging back up to 2.81v at 10am. Exact same pattern the past 2 days and similar before that depending on sunshine.

If there’s no real sun for a given day it drops a tiny bit more but not like the initial drops after it peaks.

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There is very little energy storage above 2.6V. Earlier units had a slightly lower max charge voltage to prolong the battery life over time. Basically, with all other things being equal, a Tempest which charges to 2.6V will out last a Tempest which charges to 2.8V.

As you can see from the data @GeekNJ posted it only gains about a half-day of time so you aren’t really missing much. I think WF decided that since the LTO cells have something like 20,000 full cycles before they are down to 80% of their original capacity that even charging to 2.8V won’t significantly shorten the battery life.

The field test units I have are definitely struggling more than the production units. I’m really glad WF included Field Tester input when determining the final charge parameters.


Thanks for this info…for it is helpful. It would be GREAT if they could use predictive weather for charging. Using AI, realize that the next 3-4 days would be cloudy and no charge capability, the unit would charge up fully today (a sunny day), thus giving it full power for next 3-4 dismal days. Would this ever be a capability of this unit???

Doubtful. In my location we get wildly different cloud conditions in just a few miles. I can’t imagine how they could predict anything at all.

It always tries to charge fully on any sunny day.

I have not had that experience…for I have had very bright and sunny days and it did not charge up. It only started charging if the volts were around 2.48 or below…

bonsoir moi il est monté a 2,70 maintenant avec les maigre rayon de soleil de par chez moi je suis a 2,47 depuis la mise en route début janvier

I think it used to be like that. What firmware version do you have?

station number firmware revision 160 device 134

mine is 134 as well. It charges whenever it can. I once did an experiment with artificial lighting. Charged it to 2.8V (the max), kept the light on, but the voltage never dropped (it fluctuated a bit between 2.79 and 2.81). So it just kept charging. Of course during normal operation the voltage would drop during the night.

For me, my hub is 143, and the station is 134…

Looking at your battery history graph, so far it’s never gone below 2.40vdc (from what I can see) and only hit that a few times. That keeps you in the full power state almost all the time. I have one that does the same thing and it’s very consistent. I like the forward looking weather based charging idea you suggested which is much like a smart irrigation controller shutting off when rain is coming. Maybe something they are looking at in the future.

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