Temporary invincibility isn't quite the way describe the effect of this item. The supercharge will max out your shields and for 30 seconds (?) after picking it up you'll be impervious to blaster fire but still vulnerable to physical damage. Don't expect to jump off a cliff and survive with an active supercharge, but you will be able to face down a platoon of stormtroopers or a dark trooper without worry. As long as you work fast.