18V Portable Backpack battery?

DIY

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Oct 17, 2019
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So a few power tool makes portable backpack battery to extend runtime and put the weight of the batteries on your back.
Ex 1: Makita PDC1200 https://www.makita.co.nz/products/model/PDC1200
Ex 2: Husqvarna BLi520X 36-Volt 14.4AH 520Wh
Ex 3: STIHL AR 1000 36-volt Backpack Battery
Ex 4: Hitachi BL36200 21-AMP Lithium Ion Backpack Battery, 36-Volt
Ex 5: EGO Power+ BH1001 Backpack Link

Looking to DIY my own version for 18v tools, specifically my Milwaukee, Ryobi tools. I have a few power hungry tools that would benefit from longer run times (e.g. angle grinder, blower, mitersaw).
I guess as long as my final voltage is in the 15-21v range (since 18v tools are just a 5S configuration), I should be find making a battery pack in that range.

What would be some battery recommendations if I want to match that Makita version with 1200Wh?

My thinking would be a 6S configuration using CALB CA100 3.2V 100AH LiFePO4.
With a nominal voltage of 3.2V, using 6 of them I would be at 19.2V.
Do they make a 6S BMS for LiFePO4?

In regards to the battery to tool adapter, I would just gut some old battery (I have a few 1.5Ah that I would remove the cells and solder some wires directly).

Thoughts on this approach?

PS, if Milwaukee or Ryobi made one, I would much rather buy it. But I doubt they ever will.

-------- EDIT

After searching YouTube, it looks like a few people have DIY their own for 18V battery backpack
1. Dewalt 20V 50Ah backpack
2. 5S configuration, but max voltage is only 18.5V
2019-02-12_145132.jpg
 
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