Quite a few people get away with using the Motorcycle style batteries, esp those that drag/race and want weights controlled. 'Tparker' on the Focaljet (Dezert Focus) uses one in his car, he drag races a lot, he could tell you if the small battery works well or not....
Not sure if the Contour suffers as some cars do but there have been known to be issues with some cars electrics (modules, computers etc) when the battery is relocated. If people have been doing it successfully on Contours, then there's probably nothing to worry about. I have heard this before though where a perfectly good car starts developing electrical bugs (injection, ignition issues....) once the battery was relocated....Just FYI.
