Battery Holder for Weather Station


I am building a weather station (ESP32 based).

I would like to use four-way 18650 battery holders such as these.

Could you please answer the following questions:

  • Are the battery holders set for serial or parallel connection?
  • When sin serial mode is there a BMS on board that monitors the voltage of each cell?
  • Is the output voltage (3.3V and 5V) regulated?
  • Is it possible to charge the batteries via a solar panel whilst in operation? (Without power drop-outs)
  • What type of 18650 batteries do fit? Flat head or with a top button?
  • If not fit for purpose, what do you recommend?

Sorry for the many questions but I want to avoid making returns if the product doesn’t fit.

Many thanks in advance!

Hi Luc,

Your questions are so broad that it might be best to start by building a solar power project and learn how batteries work, from charging to voltage regulation. Do away with other project complexities and solve each smaller (and more specific) challenge as you focus on power/batteries alone.

And then take those skills into other projects, such as the weather station.

You are better off selecting a single-cell LiPo, and for solar charging, using something such as this.

If you want a regulator onboard as well, then perhaps this or this.

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I want to elaborate on my initial post shown above.
Initially, I had this product-related question addressed to the good people at Core but there’s a bit more to it.
Seven years ago I designed an Arduino Mega-based weather station and now it’s time for an upgrade.
My old weather station was equipped with two 12V solar panels. The core of the new weather station will be an ESP32 connected via WiFi. Obviously, the power requirements are different from what I initially needed.
The idea is to keep the two PV panels. These panels will need to charge 4 four-way banks of 18650 batteries.
Obviously, the weather station will need to run 24/7 and cannot have any interruptions in the power supply. So I’m working on a solid power supply for the ESP32.
I was thinking of having a combination of serial and parallel battery setups. The reason why I need this many batteries is that I want a redundancy of between 3 to 5 days. I live NE of Melbourne and in autumn and winter, we can have many days without sunshine.
As Li-ion behaves differently to lead-acid batteries I have many questions in that regard.
The batteries need to be protected against under and over voltage and I also want to be protected by a BMS. Originally I was thinking of utilizing a TP4056 but that idea was canceled rather quickly as it has too many limitations. Then I was looking into TP5100 but this wasn’t ideal either.
Then I came across a CN3795 MPPT PV charge controller module and that seems to be better.
By now, you probably realize that I’m puzzled by the many options available.
If this becomes unfeasible then I’m happy to move to LiFePO4 technology. There are 12V batteries available and most of them have an inbuilt BMS, over and under protection. I just want to make sure I can charge these batteries through the 12V PV panels.
Anyway, this topic could be interesting to many people with different projects. Can somebody give me some hints or ideas on how to build this?
Many thanks in advance!

Hi Gramo,

Thanks for your fast response and great suggestions! Much appreciated.
I will look into this in more depth. Great to see that all these components are available from the same supplier.
Your suggestions got some merit to it.
Once agin thank you for the suggestions!

An appropriately sized single-cell LiPo will suffice, there is no need to add the complexities (or risk) of multiple LiPo cells.

Here is a starting point you could consider; I haven’t verified the calculations.

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Hi Lrat
Regarding the battery holder you linked

I think FLAT as per the recommended battery on the product page.

I have some 18650 holders which visually look the same construction as the ones here and batteries with nipples WILL NOT fit. even though this type is listed as 18650 (65mm long) they are actually mostly 69mm and are too long to fit into these holders (if they are in fact the same size as mine). You will need batteries that are actually 65mm to fit.

Note. Core are not the only supplier that sell holders that will not accept nipple type batteries. Everybody does the same with no mention of this in the product description. You find out the hard way. I think everyone just blindly reprints what the manufacturer publishes. At least for this device Core recommend a flat top battery.
This seems to apply to AA size also.
Cheers Bob

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Hi Bob,

We only stock the flat-top style 18650 cells and 18650 cells with solder tabs. There are other very similar batteries out there which include an internal protection module that increases the length of the cell (unsure if they are still technically as 18650 cells as the name comes from the dimensions). All of the 18650 cells you get from us should fit the holders we sell, but it pays to double-check if you are trying to use existing cells of a different length with our battery holders.

ESP32 based weather station design.pdf (139.8 KB)
I made up a rudimentary Excel spreadsheet and converted it to a PDF (The forum didn’t allow me to upload an Excel spreadsheet).
I worked everything out and it’s based on the information I received from Gramo.
I added lots of redundancy in the system and I was surprised that I could get by with a battery of 5.35 Ah and a solar panel of 0.8 W.
If my calculations are correct then it will make this project very simple and affordable.
This was a great exercise and I will keep the template as it can be used for all sorts of applications.

Hi Trent

Had noted that

They are still sold as 18650 cells. Although as you say this is technically incorrect.

I also note you are using the proper terminology “cells”. I think too often the term “battery” is incorrectly used. Including myself above but I did so as the term Battery was used initially and I did not feel like explaining the difference at this stage. This is good as I think it removes any ambiguity and can avoid confusion. A classic example is the common Sub “D” connector shell. Like many call this “DB”. What about A, C, D, E. This is a good example where the correct terminology removes all confusion.
Cheers and keep up the good work. Bob

Pleased to see you allowed a couple of 20% “fudge factors”. Good idea as every time you do a voltage conversion you could lose up to 15% of that. Call me super conservative but I personally would make this 50% or at the very least go the next available size up, never down. Depending on individual circumstances this could be 100%.

Re your Excel spread sheet. Have you ever tried a “csv” file. This is a comma (or other) delimited text file which can be loaded straight into another spreadsheet although your layout may not suit this as the first line is a list of column headers followed by each subsequent row under those headers.
Just a thought.
Cheers Bob

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After reading up on the comments and suggestions I might have come to a conclusion.

For the solar panel, I might opt for this one.
For the LiPo polymer battery I might buy this one.

Now I just need to find a suitable charger that protects the battery from over and over voltage.
Is there anything that you could recommend?
Ideally, the charger should have a 3.3V and 5V output to which I connect the ESP and multiple sensors (Some will need to run on 5V).
I also might need a buck converter that can raise the voltage to 18 to 24V (My anemometer requires this).
I don’t want to compromise on quality as I want to make something that will be reliable for many years to come.


I think that device you linked in your initial post does all of that.
Cheers Bob

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So, do you mean the CN3795 MPPT PV charge controller module would be a good option?

Don’t know anything about the CN3795. I was referring to your link in the initial post to DFR0970, the 4 18650 holder with a charge controller, over charge and discharge protection and 5V + 3.3V outputs. Have not looked into it any further. I am not exactly recommending anything at this stage.
Cheers Bob

OK, thanks for the explanation. I agree, the story has changed a bit since the original posting.
My apologies for the confusion.