Homemade power banks

During an astrophotography session in outdoors, smowhere in the field, especially in spring or autumn, there is dew.
A wet lens makes photography impossible, so you need to take care of the possibility of drying the lens and even better, prevent dew during the photo session.
A heater-tape powered from the USB port of the powerbank, is ideal for reducing dew on the lens and even eliminating it totally.

Over the years I have used a number of different, small travel powerbanks of commercial manufacture, for charging my phone or powering mentioned heater.
They all broke down after a period of two years of use except for one, which still works today. It is an exception, no longer available on the market for sale.
Each commercial powerbank broke down in almost the same way, for the same reasons. The first reason was the large amount of water accumulated on the unit (dew), led to a short circuit.
The second, more common reason for failure, was the negative temperature in which I used the powerbanks, a range of -1 to -8 C degree.

I struggled with trying myself to repair the defects once the manufacturer’s warranty had expired. For those units that survived I’ve sent with the warranty service, which most often returned my money instead of the repaired device. Every time I went to take a night shots of the sky, I wondered – which of the two powebanks would break down this time?
My irritation reached its peak, when both powerbanks died in the same night in use with -3C degree.
Commercial powerbanks that can work with negative temperatures, cost far too much in relation to the capacity and functionality they offer.

I sat down at my computer and started working on my own powerbank, that would not die during use in minus degrees. I defined my own requirements and after two months of work and after-hours digging in subject, I created a prototype that worked without much complaint. I knew that the prototype would have hidden flaws that I was not aware of. I thought, my children could be great testers of my idea. I made a copy for each of them and two pieces for myself.

Over more than a year of using all the units, design and functional flaws became apparent, which were easily corrected. During use, I came up with the idea to add a small PV panel that can charge the powerbank in outdoors under the sun light. It doesn’t give a lot of extra power, but it will always reduce a bit the power consumption from powerbank self.

My owne powerbanks I carried with me almost everywhere. I used them in negative temperatures range from -1C to -13C.
None of them failed. Only the capacity of the recycled power cells used decreased, which in most cases is typical, when you use used rather old power cells. Everything wears out. I only replaced the cells that were weaker and used the powerbank further.
Today I’m already using the new final version, which I’m very happy with and I’m not going to buy any more commercial powerbanks, that don’t meet my expectations.

It has only one disadvantage, it is a relatively large device compared to commercial ones of the same capacity, some how I had to pinch all the electronics, replaceable power cells and PV panel. Personally, the size doesn’t bother me. When I go outdoors to take photo shoots or for any other reason, I throw the powerbank in my backpack or bag and vayola ahead 🙂

The photos show power banks that I made for my children 🙂

The main functionalities and capabilities of the powerbank are:
– replacement of used cells with new ones, without replacing the entire powerbank, definitely reduces the cost of using it,
– use of different capacities of power cells available on the market. I can increase or decrease the capacity of the powerbank, I rather prefer to increase 😉
– PV panel always helps a little in charging devices and saves energy in the powerbank itself,
– USB-A charging ports support fast charging mode,
– ability to charge the powerbank in fast charging mode via the USB-C port,
– ability to charge the powerbank in standard mode via the micro-USB port,
– % level display of available energy.