Having done what the JD3 can do with a Battleship...I must say, its very overpowered. I will admit, it's fun to jump out and come back to finish tanking more Dreads and jumping out again...but it isn't fun for others who have to deal with this. I actually sold my Jump Drive for that same reason, because it doesn't make a fair fight for the other side ( unless its a gank, then I don't care if I used it ).
Having used the device...30 seconds to charge is very fast, since you evade for that time ( even in a Turtle, it's possible ). So increasing time for it to charge, might be a better solution, because all JD3 users, use it at 30%+ Hull left. This will change their timing a lot, since most of the time when you jump out, you have 5-10% hull left. Maybe making it another 15-20 seconds longer to charge, could be 'killable battleships'.
Then, you can try making a rule, if you are exploding while jumping, it counts as PvP Death...since it happens a lot, and it shows you died in another system and not the one you were fighting in.
There are a lot of ways to make the Jump Drive not completely useless, and not super overpowered. You can always make it to have the one with the Jump Drive, to think harder about his tactic, and not just charge a fleet and type /charge and /jump after 30 seconds. In 30 seconds, it's possible to kill a Battleships...but you would need 2-3 Battleships shooting that one with the Jump Drive.
You can also make it use more fuel, which will make the owners use lower armors, making them die faster and possibly even get killed before jumping. Currently, you can use a Turtle, Cap 7 and MOX to jump one way, or Cap 6 and Fuel for one way. With Cap 6 and MOX, you can jump two ways, so...can jump to like Texas into battle...and then back to Koeln or wherever the MOX sells.