BMW Problems

It's unlikely to be the battery, as you've proved when the fully charged one didn't fix the problem. BMWs of that model had problems with the ignition switch and I would suspect that that's your problem. Next time it happens rapidly turn the switch on and off several times and see if you get any response. If you do it's the switch that is your problem.

It could be a number of things, possibly worn suspension bushes, but you should have it checked out by a mechanic to get a more accurate diagnosis.

The X5 would be my pick because it's a classy car that was the class benchmark until the current Mercedes-Benz ML arrived. But make sure you do your homework, as any complicated prestige car can get expensive if something big goes wrong.

Good to be of assistance in resolving the problem. Resolutions are usually best sought from the selling dealer and carmaker.

Ten grand is very cheap for an X5 and the lack of history rings alarm bells. Even a single major problem could double your spending. Steer clear unless it gets a massive tick from a motor club pre-purchase report.

Definitely go for the Volvo. Apart from the safety gear, it's well built, well equipped and drives well.