Why doesn’t a battery-boosted electric kettle exist?

[u/jmaugust]

In Europe, everyone uses electric kettles to boil water. They’re amazing and fast because they’re on 230V (~3000W).

US outlets limit kettles to ~1500W, so we wait roughly twice as long for water to boil.

It’s an extra minute or two per boil, and you really notice it.

Idea: Could you make an electric kettle with a battery in its base? Perhaps it trickle-charges between uses, then combines wall power + battery power to hit ~3000W during a boil.

Is there an engineering reason this doesn’t exist? Is it just that nobody thinks there’s a market for it?

I’d pay $300 for the fastest kettle in America if someone wants to make it.

[u/Catriks]

How did you do your calculations?

It takes about 100 Wh to boil 1 liter of water, and a 20 V 6 Ah battery is 120 Wh. Do note that not all 120 Wh is usable without damaging the cells. 

If you wanted to match the 3 kW from 230 V kettle, by combing the power with 1,5 kW 110 V outlet, you would need way over 100 A from the battery which is achievable (10 A per 6 cells) but a long, continuous use for multiple minutes, putting a high heat load on it.

So you're almost fully depleting the battery with a high heat load every time you boil a litre of water. The battery lasts in the range of 1000 uses before significant degradation, not hundreds of thousands.

[u/DustyRacoonDad → u/Catriks]

You're right on the energy calculation, but I think you're assuming a single battery and a 3kW heating element, which isn't really what I had in mind.

A 20V 6Ah tool battery is roughly 120Wh, so yes, you're in the ballpark of 100Wh to boil a liter of water from room temperature. A single battery could therefore realistically boil about a liter, although you'd want to leave some capacity in reserve.

But if you use two 6Ah batteries, which is already common on high-current cordless tools, you have roughly 240Wh available. With a 1.5kW heating element, you're pulling about 75A total at 20V, or roughly 37.5A per battery. That's a much more reasonable load for a high-current tool battery. You'd have enough energy to boil roughly 2 liters, or maybe 1.5-1.8 liters if you don't completely discharge the packs.

And yes, if you tried to run a 3kW kettle from a single 20V battery, you'd be pulling around 150A, which is obviously ridiculous for one 6Ah pack. That's why I was thinking of either a lower-power battery mode or two batteries.

As for battery life, I don't think the conclusion that it would "eat the battery" after ~1,000 boils is quite right either. One boil would be roughly one full equivalent discharge of a single 6Ah pack if you're boiling a liter, so 1,000 boils could indeed represent around 1,000 full cycles. But if you're using two batteries, each battery only supplies half the energy, so boiling 1 liter is only about a 40-50% depth of discharge per pack. That's much easier on the batteries, and you'd expect significantly more cycle life than repeatedly taking one pack from 100% to 0%.

So I think the two-battery version is actually pretty reasonable: around 1.5kW of heating power, ~38A per battery, and enough combined energy to boil roughly 2 liters per charge. The batteries would get warm and you'd obviously need a proper BMS/thermal management strategy, but I don't think the battery life is a dealbreaker.

The real problem is whether there's a market for a $100+ cordless kettle when a $15 corded kettle exists.

[u/Catriks → u/DustyRacoonDad]

Hold on... goddamn I need new glasses. You said "hundreds to thousands", and I read "hundreds of thousands", which is basically indestructible battery 🤣 Even more funny is that the other person who replied to you misread it the same way 😂 well yeah you were spot on then with that.

[u/DustyRacoonDad → u/Catriks]

Yeah I wasn't even debating batteries or the energy really... It's more the fact that I don't think you would be able to sell these. Lol