Thank you. I appreciate your comments.
Before I decided to create this hat, obviously I was looking for a UPS solution that matches my needs. As you said, there are a lot of solutions, but I couldn't find any with integrated batteries (except one, with a higher price). All I found had a separated case for batteries (as the example you indicate) and many of them were only spare batteries, without any control (when batteries charge was low, RPi turned off abruptly). That's exactly what I didn't want.
About the price, yes. It is not cheap. When I planned the price list, my objective was not exceed 20€ per hat, but it was impossible for the quantity I can handle. Anyway, all UPS hats I found have a similar price, and without batteries
(as the example you indicate). I'm not saying they do not exist. I'm just saying that I did not find any.
In summary: if you are looking for a secondary power supply, maybe this is not your best solution, because it is not designed to hold a lot of minutes or hours. If your needs are a system that avoids an unexpected shutdown and compact enough to fit all the components -battery included- in a small case, this is a good solution.
Ongelma wrote:"maybe never completing kickstarter"
If I reach the objective, the hat will be made, 100% sure. All the hard work -design, programming and tests- was made. The money I'll get is to ensure the fabrication costs. As I explain in the project description, if the objective is reached I plan to make a minor changes, like further reduce the size and move the USB connector.
In fact, you have given me to think, and I'm going to study the posiblility to fit this hat into the "official" RPi case. The measures fits. I'll check what can I do with GPIO port.