If the unit is plugged in and the battery isolation tab is not fitted and the battery voltage is low the AIHD will not start and will sit there with just a blank screen appearing to not do anything, until the battery has sufficient charge. 

* Note this could be up to 2 hours.

If the unit is plugged in and the battery isolation tab is fitted the unit will start irrespective of the charge on the battery. The battery tab can then be removed and the unit will continue to function.