[BarnRat]

Optimate 4 is tried, tested and frequently recommended on this forum, so that more than anything else would make me buy Optimate. I've had an Optimate 4 canbus edition for 4 years now and it's kept my 9T's battery in good nick and plugs into the accessory socket without fuss.

No idea about the BMW charger, but I'm going to guess it'll be more expensive and probably not offer more than the Optimate does...

The BMW dealership here only stocks the Optimate 4 -- if I wanted the BMW canbus charger, I would have to order it. I got my Optimate 4 from Amazon.

 

[BarnRat]

What about a Battery Tender direct to the battery?

That's what I did with my new R9T -- it was easy to hook up an SAE connector under the seat -- took all of 15 minutes.