Nope; either the information is not available to Javascript code at all, or the Javascript code can do whatever it wants with the info. A security permission,

Nope; either the information is not available to Javascript code at all, or the Javascript code can do whatever it wants with the info. A security permission, or config setting, can/should be used to prevent access to the api that returns the battery level. But once access is enabled, there's no way to prevent the code from getting the level (which is just a number) and sending it to a server (which is just calling an ajax request with a numeric argument.)