Due to a common embedded controller found in Lithium Ion (Li-Ion) and Lithium Polymer batteries and used in a large number of MacBook, MacBook Pro and MacBook Air laptop computers it is possible when the battery is "unsealed" to conceal data in its memory. To avoid data being lost at the next boot up of the laptop, by setting the unsealed battery's embedded contoller into Boot ROM mode (factory setting stage) charging cannot function and pass information to the flash and overwrite the hidden data.  Link: Mobile Telephone Evidence