This would be really great if it ever hits production, but given past battery progress vs what's actually available, I'm not holding my breath.
A significant amount of that weight is the battery, so making the battery 2.5x heavier would make the phone substantially heavier, even with the same overall charge. You'd be hard pressed to sell someone on 'This new phone we made is great, you get the same battery life as before but it weighs 40% more!'
I suppose the question is, in which cases would people be willing to accept a lower charge capacity if their phone could charge to full in, say, minutes rather than hours? I feel as though those USB battery packs that are everywhere these days would be a great candidate; plug it into the wall for a few minutes and you're fully charged, and you can charge anything else from there.
It's actually super easy, you just say things like "solid construction", "substantial", and "build quality".
"Beats By Dre headphones teardown finds metal parts included just to add weight"
I know your comment is a bit tongue in cheek, but an LED connected to an AA battery is enough to last a few days - IKEA sell a nice set that even flickers. I don't go to church, but I suspect the flame (fire) itself is symbolic.
It's actually friction, for electric cars. Regen is pretty effective at recapturing acceleration, so the energy lost in the wheels is the biggest factor.
Mass counts much. It's not just about accelerating a still object (car) out of friction. But it's also about working against gravity (g). If the car's acceleration vector is at some angle with gravity (ie, when not perpendicular), more energy will be required to accelerate (when climbing slops), and to break (down the slope).
This is very much clear for aircrafts, and other flying objects.
Edit: Inertia is also a reason for energy loss in cars (and other moving objects), which increases with mass.
Rolling friction loss is related to speed and is occurring constantly as you drive. That energy is just gone immediately, unlike inertia, which is stored. Say you spend 50% of your time accelerating and braking, and 50% keeping speed. If you regen 80% of the energy and accelerate with 2.5x the power you use to cruise, you're using twice as much energy on friction as accelerating.
I don't know how good exactly electric cars are here, but considering that a Tesla can work as a taxi in the city, it must be pretty good.
[edit: punctuation]
Unless these batteries can accept charge faster, their extra mass won't be offset by more regen.
The same reason city driving is less efficient?
That's just the voltage across the terminals. The reason why this works is precisely because current doesn't go from 0-100% with the voltage. PWM is relying on the inductance of the motor to keep the current the same as it would be if the average voltage was applied across the terminals.
Submersibles (which may not care about weight due to ballast anyhow), Batteries for Solar Storage (price dependent likely bad at first), Pacemakers, Hearing aids, once it's invented if robotics outpace man engineered human biology, maybe smart blood.
Perhaps also Nanobots, Active 3d Glasses, Cell phones, Laptops, Tablets, Smart Watches that go for smaller space vs weight.
Outside of that perhaps home appliances like a portable bread machine, or a hand-held wireless electric apple peeler, very small things like a rock that has a hidden microphone / camera in it for spycraft, perhaps a heated travel mug to keep your cider warm, or an electric bowl for keeping great-gravy from coagulating on the dining room table, maybe a warm pie plate because who doesn't like warm cherry pie? Perhaps some sort of autonomous mud tunneling microbots, rather have a large boring machine just let these small guys go and be patient and in a decade or two you'll have your tunnel, electric candles in churches could cut down on unnecessary wax use, and helmet lamps used for stuff like lead mining could also find a use (added neck strain not withstanding). Not sure if the added weight would be too much for a target-practice duck that swam around in a lake or not, but if not, that might be the right answer.