DolboD

why do you need arduino if you use raspberri bi? it would be cool to use just arduino and run the homekit server there

Oh man, trying to read through this, this is overwhelming. I wish you had a short text separately, you just the design with the key points outlined without things like what a mosfet is. I just read up to the point where you say micro is too slow so we don't use a micro and use an opamp instead but next thing you describe ADC, DAC etc. So is this a micro based approach or not? Thanks

What kind of battery are you charging? It doesn't need constant current in addition to constant voltage?

Maybe it works but the instructions are not very good. Lots of big pictures but no technical overview. How does GPS send text messages? How do you talk to it? What kind of subscription do you need to have? How much does it cost? Etc.