I love the idea and thought I'd do a rough check on the math:
Assuming the goal is to match the power delivery of a high power UK kettle, looks like the batteries will need to step in and produce about 1kW of power for the duration of the boil, something like 50% on top of the standard 15A US circuit. I know on paper the circuit ratings are nearly 2x, but in practice it sounds like it's closer to 1.5x for the average kettle comparison.
80% efficiency for the heating coil, 1.6L of water, you need about ~750kJ (200Wh) get to a boil from 10C tap water.
So you'll need at least 70Wh output from your battery, and it needs to provide 1kW continuously. Accounting for conversion losses and some buffer to avoid deep discharge I'll target 80Wh. At 1kW that's a continuous 13C discharge rate, which is pretty high. Hobby-oriented LiPo packs will do it, but I'm not sure how they would hold up for consumer product safety and longevity. LiFePO cells could be a good choice since density is _less_ of a concern, and are readily available with 20+C continuous discharge.
I don't know my power electronics very well, so I'm not sure the best way to merge the outputs. Any conversions are going to eat into total power and thus boil time, just rectifying the AC will take 20%. Maybe it makes the most sense to have two separate coils, one direct from AC and a second from the battery? With smaller cells in series, say 10+, to get a decent voltage it could end up with a manageable current to use directly with the 1kW boost. In that case the only expensive power electronics needed would be to charge the batteries.
Also have to figure out how much recharge time matters to people, since by default it would be an hour or so.
It's going to have a chunky, heavy base, and guessing it will have to be pretty expensive for what it does, but I like it.
The whole idea sounds pretty insane really. Who's going to pay hundreds of dollars for a battery-powered kettle just so they can save 1-2 minutes of time (and less if you're just making enough boiling water for 1 cup). I use a little 100V (900W I think, according to the label) kettle to make tea, either 1 or 2 cups at a time, and while it's certainly not as speedy as those EU/UK market kettles, and a bit slower than a US kettle, it's fast enough.
A battery-powered one might save me 1 minute of time at best, but will cost probably at least 5-10x as much for the kettle, it'll be MUCH larger than my current kettle (that battery pack and power electronics needs space) which is a problem with my tiny kitchen, and I have to worry about how long the battery will last and how to dispose of it later and if I can even replace it.
There are lots of products that aren’t _necessary_ at all but bring an amount of fun to the world. This feels to me like one of those. Not convinced it could even recoup development cost, but I’d be happy to be surprised. There’s certainly a niche for well off Brits (and EU folks) living in 120V land hankering for a fast cuppa.
The reality of product development and manufacturing is that economies of scale affect prices such that low sales quantities (i.e. a "niche product") generally means extremely high prices. Also, the BOM cost alone is probably going to be high, because of the huge batteries needed (with high current ability) and the power electronics involved. Then when you consider the safety ratings and certifications needed (since this is something that could easily start a fire with the power levels involved), I don't see how it could be sold at any kind of reasonable price unless there's a really big underserved market.
Sure, if this device could be sold for USD$50, it might sell some to people like you say, but how many of these people would spend $500 or more on it?
I'm supportive of the original idea because I think it's fun and cool. I agree with everything you've said, but we're talking a bit at cross angles. You're looking at it from what it would take for this to be a successful, competitive, and profitable consumer product. I'm looking at if it is technically feasible and can be made for non-absurd amounts of money. Our threshold of non-absurd may also differ, but given there are some people will pay $20k+ for an espresso machine, there are likely some who would pay several hundred dollars for a tea kettle.
Sure, it's technically feasible, but I'm questioning if it's financially viable at all. Being fun and cool isn't all that great when you end up with a product that just has some prototypes and a bunch of hype, but then the company goes bankrupt before it goes anywhere. There are some examples of things like $20k espresso machines that were successful, but I think they're rare.
Assuming the goal is to match the power delivery of a high power UK kettle, looks like the batteries will need to step in and produce about 1kW of power for the duration of the boil, something like 50% on top of the standard 15A US circuit. I know on paper the circuit ratings are nearly 2x, but in practice it sounds like it's closer to 1.5x for the average kettle comparison.
80% efficiency for the heating coil, 1.6L of water, you need about ~750kJ (200Wh) get to a boil from 10C tap water.
So you'll need at least 70Wh output from your battery, and it needs to provide 1kW continuously. Accounting for conversion losses and some buffer to avoid deep discharge I'll target 80Wh. At 1kW that's a continuous 13C discharge rate, which is pretty high. Hobby-oriented LiPo packs will do it, but I'm not sure how they would hold up for consumer product safety and longevity. LiFePO cells could be a good choice since density is _less_ of a concern, and are readily available with 20+C continuous discharge.
I don't know my power electronics very well, so I'm not sure the best way to merge the outputs. Any conversions are going to eat into total power and thus boil time, just rectifying the AC will take 20%. Maybe it makes the most sense to have two separate coils, one direct from AC and a second from the battery? With smaller cells in series, say 10+, to get a decent voltage it could end up with a manageable current to use directly with the 1kW boost. In that case the only expensive power electronics needed would be to charge the batteries.
Also have to figure out how much recharge time matters to people, since by default it would be an hour or so.
It's going to have a chunky, heavy base, and guessing it will have to be pretty expensive for what it does, but I like it.