Cymek said:

I asked a question the other week (I think so anyway)

Do batteries have an upper limit to what they can store and not actually be hugely unstable.
I’d assume it likely depends on what we discover and create into the future.
Science fiction has hand held devices that going by their destructive capabilities must hold many megawatts of power
Wondering if its even possible without violating the laws of physics

Google..

The theoretical maximum energy density for a rechargeable lithium-ion battery is roughly 400–500 Wh/kg.