I replaced a battery once without the bracket because I lost one of the screws and it was fine for years (non-Benz), but I'm not sure how it would affect this car. If it feels OK, it probably is for a short time, but I would find a way to secure it. If it is movable, I think it would eventually cause stress on the terminals and wires.
Also, you should update your profile with your car type before people on this forum give you a hard time. Also a word of advice, you'll get pounded for asking questions for information that is already posted, so try the search function first.