Underpowered battery tools? Yeah, I know that for this fact: 24 chinese volts drill battery pack overhauling…
Of course, even if the nominal voltage wasn't increased, for me there's little doubt those NiCads couldn't even dream of remotely delivering half of the current the new pack can without breaking much sweat. Additionally the staggeringly improved capacity allows the operator to do a lot of work with a single shot.
Batteries seem to be one of the expensive parts of a tool, thus high quality li-ion packs may be hard to find inside cheap toys. If enough space is available inside the battery tray… dream on! For the above tool, doubling both voltage and current delivery could be done with a 4S2P pack of HE2s/VTC5s and 2 × 30A BMSs in parallel, but that would probably mean motor meltdown LoL! 
Cheers ^:)