I'm actually surprised to read so many negative comments about technical issues with the g650
I bought a used, but relatively new g650gs in 2016 (build '14, first owner BMW, 2000km) and put 70000km on it so far - literally without losing one single bolt. And it really had to take some beating, lot's of rough ground, offroad, water crossings, the whole bit.
The "chinese Rotax" is just working, no oil consumption, no leakage, nothing. It had a strange phase with quite heavy vibrations around 50k, but it just came and went.
The only electrical problem I ever had was a broken clutch switch (the one at the lever).
The cover of the front brake fluid container tends to leak, I recently changed to the third one.
So much for the problems I had...
Just to mention, the hot-start-issue was fixed around '13, afair BMW offered free replacement of the worn out choke or just changed it when servicing. Mine doesn't have this problem.
Regarding possible battery issues: I had a Gel battery from day one, a gift from the shop where I bought it. It's still in there & I never cared about it.
There are a few downsides though; as already mentioned the rear shock "isn't really good", same as the fork. I changed to Touratech suspension last year & really wish I had done this earlier. Not saying it has to be TT, I guess any rear shock will be better
Maintenance is indeed a pain - or expensive. I sometimes think the engineers where told to hide anything as good as possible to prevent self-service... Anyway, it has a 10k interval, so I can cope with it. And, to be fair, I heard about similar maintenance nightmares on others bikes as well.
I'm definitely NOT a BMW fanboy, not at all. If my legs weren't that short, I possibly be riding a 660 Tenere. But I'm really happy with the g650, and I'd always! buy it again. Mine is definitely a always-works-never-lets-me down bike.