Finally I managed to buy a working second-hand Nexus5 motherboard (shame on you, :-), you who sold me a smartphone 'for spare parts' that clearly had suffered severe water-damage and had hardly any parts to salvage, and you who sold me a 'to be tested' motherboard that turned out short-circuited and of which a component had clearly been stripped off) and I'm back in UBports business.
When my motherboard initially died, I should have probably dumped the poor phone and bought a more recent UBports compatible model, but for some reason I had grown attached to it and, also, my stubbornness to want to fix it grew with every failed repair attempt.
Still, there's a love and hate relationship between myself and Mr Hammerhead, as the poor battery life still keeps frustrating me. For that reason, I'm planning to now find a Nexus 5 battery case.
Sadly so far the relevant e-commerce sites I found, either list the cases as discontinued or don't ship to Europe (e.g. https://shopbastex.com/collections/zerolemon/products/lg-nexus-5-zerolemon-extended-battery).
Another solution would be to create a battery case myself, by attaching an external battery to the inside of a universal wallet case, and by connecting it with a small microUSB cable to the phone. But in my experience the weak link would be the USB cable getting loose or damaged easily. And I also have a bad experience with a previous wallet case, where the sticky patch got dirty and lost its 'stickiness' too soon.
Finally, a third option would be to attach a wireless external battery when needed, something like this one: https://www.alibaba.com/product-detail/OISLE-Ultra-Small-Cell-Phone-Portable_62386010726.html?spm=a2700.wholesale.deiletai6.5.67426b65ygx15i.
Any advice or experience with specific models of battery cases or of wireless external batteries to share? Thanks!