Good on ya
I have a handful of those mini-USB cables cut up in my spares box, the ones you buy nowadays are built down to a price (sub-$1) and are absolutely atrocious.
I fixed a similar GPS last month for a friend, his cable frayed and was making intermittent contact, of course this drained the battery, eventually killing it. Replaced the battery and cable, new cable was crap. Replaced the cable, turns out his car charger died as well. (lifted positive trace)
I politely asked him not to bring me anything more complicated than a rock to fix next time.