The problem with better and better batteries is that those better batteries come with inreasingly dense chemical energy, which makes them more useful but also more dangerous. Lithoium-ion batteries are within the same order of magnitude of chemical density as TNT! To make matters worse, lithium-ion was delayed to market for years because they catch fire so incredible easily from overcharging and overdischarging; it wasn't until protective circuity was developed that they became widely adopted.
Anecdote: when lithium-ion batteries first made their way into cell phones, pilots of ultra-light indoor R/C planes would dismantle the battery packs to put them on their planes, removing all the protection, but carefully sizing the motors and all to within the same limits of the battery. But if the propellor happened to hit something (like the ground) while the pilot still had the throttle on... that locked-rotor current would send the Li-ion into thermal overrun within seconds. They had a similar problem with charging. The fancy smart-chargers will let you dial-a-setting... and if that setting is too high... heh.
Apparently, the Tesla roadster offers supercar performance from its li-ion battery... but don't try to track it, because under race conditions, the battery will overheat and catch fire!
