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Comment by IgorPartola | Hacker News Reader

The entire product weighs 0.5 kg, and it is 0.7A at 3.6V. I assume the amp rating is really amp-hours, which would give it 2.52Wh. Figure the battery is half the weight of the tool, which would give it roughly 10Wh/kg.

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According to https://www.sciencedirect.com/science/article/abs/pii/S03787... the batteries Tiamat produces are 18650 format, 3.7V, 0.61Ah. The latter more or less matches the specs of the product. This would mean the product might have a single 34g battery with a specific energy of 68Wh/kg, and 135Wh/L. So low end of nimh. Which sounds somewhat reasonable, 10 (and around 20Wh/L) I don’t think you’d bother even going forwards with.

Sadly I can’t find any teardown of the product, it’s all just press reprints.

There’s a split view PDF (in the documents section), it doesn’t seem to show the battery but does not show a huge amount of space for it.

I got the same 68 Wh/kg from this report: https://www.greencarcongress.com/2023/10/20231030-tiamat.htm...

Low end of Nimh doesn't sound very great, but - what if you could get 18650 cells for (making up a small number) $0.50 each? I think I would end up with a box full and just swap them as I use them. Even better if they retain charge well.

It has other great advantages over NiMH: fast charging, no memory effect, no self-discharge

Absolutely! However my baseline are my Li-ion 18650 cells which have those advantages as well, in addition to larger capacity. But I think I would be willing to give up the capacity if the price was much lower.

Yeah, considering the tradeoffs it has to be much cheaper to be worthwhile. I would say 5-7 euros per cell retail to be worth considering. Otherwise why bother ?

NiMH doesn't have noticable memory effect. NiCd does.

NiMH self-discharge is low enough to not matter for most applications. 5th generation Panasonic Eneloop is 90% after 1 year of storage, 80% after 3 years, 75% after 5 years, and 70% after 10 years.

This paper describes Tiamat's battery as Na3V2(PO4)2F3:

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10....

How much of that weight is the essential weight of the battery, and how much is consumer-friendly outer shell, electronics, other one-offs etc.? I.e. if you wanted to take the same tech, put it in a non-consumer-facing context (say a grid-scale battery) and wanted to make it 100x the capacity, would it be 100x the weight?

I can imagine a lot of the weight of the battery unit itself isn't necessarily the battery, if that makes sense.

The spec sheet on the store is confusing. It says :

Intensity(Ah) Less than 1.5

Tension (V) 3.6

Amperage (Ah) 0.7

Edit : the box indicate 0.33 Kg, the 0.5 weight probably include the charger and other parts.

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