It is not required, and there is a small issue that a few customers are experiencing which is temporarily solved by unplugging the battery. That will be permanently solved (allowing those customers to plug their batteries back in) in 3.2, which releases next week barring any last minute bug-finding.
Having the battery does keep SkyView working if your electrical system fails. The other big advantage: in some aircraft, voltage will drop below 10V momentarily during engine crank. This will cause SkyView to reset, which takes about 20. If you don't have the battery, your engine information (particularly oil pressure) won't be available during that critical time after engine start. So many customer opt for the battery for those reasons.