A char limit textarea used is various datatype/prop editor examples around the years now available for Belle
You need to run a build of Belle that has the commits of 17/9/2013 in them since there have been some changes (prop editors require a unique alias not a guid anymore)
Simply drop the folder in the /App_plugins folder of your Umbraco Bell instance, restart the app and you should be able to create a new datatype and select char limit as the propery editor.