Help me choose the right Batteries 🔋

Hardware
1

Hi, :wave: will get straight to my issue. I am trying to choose the correct type of batteries to power up Arduino Nano + GY91 + uBlox GPS + LoRa RF Module + 3x Micro Geared Servos + 2 Micro Geared Steppers (via DRV8833).

Together this setup will be attached to a High Altitude Weather Balloon and hopefully reach up to 35km of high - TEMPERATURE is a huge factor here and with recent knowledge, I must rule OUT NiMh batteries (like the one I've got already)

By the shopping list, you can tell, I am a noob :smiley: When I bought the NiMh batteries the model shop didn't have any chargers for it so I decided to go rough and get on online, even better Solar Panels with solar charger .... only if I knew it's NOT for NiMh batteries :smiley:

However, the 6v NiMh batteries did a great job powering my 2 servos on the breadboard for prototyping and testing but when I reached the assembly I hit a stone :smiley: and this is a big one... I was happy to use NiMh due to their weight ... perfect ballast...

So, is LiPoly an option for me? The expected flight time is around 2 to 4 hours where servos and stepper motors will work only 1/4 of the flight time. The main thing is the Arduino, GPS, Gyroscope, and the LoRa module, aw and we also have 5 solar cells (5.5V 60mA) that I love to use in this project :smiley:

Any suggestions are welcome. Thanks For Looking!

2

Lipos don't do well in the cold, either. At least not the ones in mass market hobbyist applications like RC cars. The hard case packs in professional drones have a heating feature (don't know how that works though) that overcomes this limitation. If you had a way to keep it warm, even a chemical type thing like the inserts used to keep your mitts warm (Hotshots) but they may not last long enough. Sorry (from Canada) that's all I've got. Maybe try a Hotshot type solution and test it in your freezer?

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3

Throughout the stratosphere we see an increase in temperature with altitude primarily from ozone absorption of UV energy. The tropopause (layer just below the stratosphere) is about -55 degrees Celsius. At the top of the stratosphere the temperature is around -3 degrees Celsius. 30 km is about the middle of the stratosphere and so it the temperature is going to be somewhere between -55 and -3 degrees.

By default, lithium polymer cells are designed for a temperature range between -20 and 60 degrees Celsius. Temperatures between 0 and 45 degrees Celsius should prevail when charging the cells.

Does not look like a good match.

4

The most common batteries for use in high altitude balloons are the Lithium Energizer AA or AAA batteries.

Good down to -40C.

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5

This is actually pretty good idea using one of those PTC Heating Element - 5V 40°C and try to keep it warm... that's only if I can insulate the whole thing.

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6

Insulation is easy enough.

You can get foam boxes designed for the purpose;

Or use one of those polystyrene boxes that stuff gets delivered in and you normally throw away.

7

The best batteries for use at low temperature are lithium thionyl chloride. These are primary cells which are used in outdoor applications such as water and gas meters that have to operate for up to 15 or 20 years and down to say -40C in some countries. Disposal can be iffy so use in a balloon might be an issue.

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LiPo4 have worked well for me with my solar project.

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