What are the limits of energy density? [closed]

I'm writing a story where in the future bullets have become obsolete as batteries have become cheap and very energy dense, so much that making defensive lasers that are able to vaporize bullets before they touch you its plausible. So the question is, is this even possible? How much energy you could pack in something the size of a cellphone battery? Given a lot more space, say the size of a car, could you change the course of the bullet so the vapor doesn't hit you?

• If you solve the storage of antimatter, E=MC2 is the formula. Your battlefield will smell of plasma instead of gunpowder. Jun 18, 2018 at 17:37
• How far out of the edge of the theoretically possible technologies do you want us to go with the technology here? Because if we go the limit the answer is really "sure whatever you like". There are even pieces of tech I can think of that exceed mass/energy equivalency.
– Ash
Jun 18, 2018 at 17:41
• @Ash, what kind of device could do that? Jun 18, 2018 at 18:16
• @Gryphon Peter Hamilton calls them Niling D-Sinks I've seen a couple of other treatments that amount to the same thing; basically you create a pocket universe and stuff it with energy. In theory it can hold as much as you like at mass/energy density without weighing any more than the interface device that gives you access to the pocket.
– Ash
Jun 18, 2018 at 18:22
• @Gryphon In terms of artifice yes, the mathematical practicalities are there, mostly anyway. That's why I asked how far down the rabbit hole the OP wanted us to go because once we start getting out towards the edges of current mathematical theory there's some really weird technology to be considered.
– Ash
Jun 18, 2018 at 18:40