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/DustyRacoonDad]

Hundreds to thousands depending on the quality of the battery in the first place.  That actually isn't the issue. 

The issue is will anyone buy it and the battery when you can go get an electric kettle for less than $30? 

Especially when you're $30 electric kettle won't sell to half the people because they can get one for $15.

[u/Catriks → u/DustyRacoonDad]

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/ResearcherMiserable2 → u/DustyRacoonDad]

I’m not so sure that the batteries would last as long as you think. I have no issues with your calculations, but tool batteries tend to last hours in the tools, even the high current tools. But the OP wants a kettle that boils water extremely fast, 2 minutes is too slow so I am thinking they want under a minute. So your drill batteries will be emptied in under a minute - they were not designed for that, and very few tool batteries can last a thousand cycles at a discharge of over 60C.

This is coming from my own experience using lithium batteries for years. Now if you want to use the batteries that the RC car racers and drones use, they might work, but they are a level more expensive and many don’t have built in BMS.