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Radically improving battery life may prove to be a more difficult physics problem than wireless charging. Lithium-ion batteries were introduced in the early 1990s, and for 20 years nobody's been able to come up with a better technology.

Since the early 90s, CPUs have gotten about 1,000 times better. Batteries have gotten about twice as good.

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2W smartphone-sized betavoltaics battery is practical, with a possible lifetime of several decades. The problem is it would be a regulation nightmare.

Yea. Batteries are a tough problem.

A battery with the energy density of TNT would be great. Not sure I'd want it sitting on my lap...

You already do. Lithium-ion batteries have 25-50% the energy density of TNT.

https://en.wikipedia.org/wiki/Energy_density (to fill in the missing volumetric density entry, you need to know that TNT has density 1.7 g/cc)

Think you're referencing Lithium (non-rechargeable) batteries. Lithium Ion is much lower.

Even then, they still occasionally overheat and very occasionally catch on fire.

I think my original point still stands.

At 4.6MJ/kg TNT is fairly low energy density compared to e.g. Jet Fuel at 43MJ/kg.

This still makes me think the future may be in fuel cells more than it is in batteries, but by now we were supposed to have fuel cell powered cellphones and laptops and it didn't came to be.

If you include the weight of the oxidizer, it's a wash. Oxygen, with mass 16, is pretty heavy compared with carbon's 12 and Hydrogen's 1 when you have to combine two oxygens with each carbon and one with each pair of hydrogens.

The big win in "energy density" from normal hydrocarbons is that the oxygen is freely available from the atmosphere.

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