Congrats on your new project! While it may be possible to upgrade a Mitsubishi i-MiEV battery, it won’t be easy and it will likely cost a lot.
In fact, just replacing a Mitsubishi i-MiEV battery can cost as much as $3,500 to $8,800 for the parts alone. Upgrading the battery is a much more complicated process that will involve reprogramming your i-MiEV’s software—you’ll need to make sure every component of the electric system works with the new battery, too.
Since you’re not super familiar with the i-MiEV’s battery, it’s safest for you to get some help from a professional mechanic if you do decide to tinker around. Not only is it dangerous to deal with the battery’s high-voltage when you’re not sure what you’re doing, but the battery pack itself can weigh over 500 lbs.