what is different about the upgraded defibrillator. Is it faster? Does it do more damage? I can't tell. Im only on the second one from Dr K but it seems pretty much the same as the one I already had

thats lame, i thought it gave you 2 charges instead of 1. my game broke before I got to dead city, had to start from the beginning....

I also saw you get another one (dr k + guy in bar) for upgrade, so thats 2 upgrades? what does it do?

It means you now have two defib charges instead of one. You can now 'die' twice in a short time period before it's game over.

The upgrade from the guy in the bar decreases the time it takes to recharge defib from 6 to 5 minutes.