ok, now that ive opened the blown gens ace, there isnt anything special inside the pack to prevent reverse polarity. i think what happened is it just instantly melted a little dab of solder used to bridge the battery to board connection and the bullet. so maybe someone designed it like that, or it was just a fluke..
i would still recommend the gens ace packs for the money though. and they always go on sale for under $30 so good value, even if you have to replace them once or twice ha.
getting a couple of those nano techs there to try, though a little nervous about taking them to a organized race as they arent approved.. but we will see. got one gens ace still alive.