I have couple reviews of the Dremel on my site you can check out if you want, and also a guide on how to use Fein blades on the Dremel. From what I have been reading, the Bosch 10.8 volt version will run about 8 minutes on a single charge. There is also a third version from Rockwell, and a forth found only on ebay. Stay away from the one on ebay, as they don't sell replacement blades, and it is from a no-name company.
Hope this helps