Yea that’s basically the reason why I can’t use a VPN.
In fact there isn’t really a problem to leave your phone connected to the selfhosted VPN all the time. If split tunneling works properly, only traffic that access your home network would actually go through the VPN, all others will just get bypassed.
But in my case, I already need to be connected to another VPN most of my day, so can’t really go this route.
It’s 12V so I guess you can Frankenstein something with a car battery. But honestly this sounds more like a LTT video than something I would trust not to burn my house down.