Tool Battery Possible as Battery Bank for Solar?

[jayson0333]

Hi guys, it's my first time posting here and I know that this might seem like a weird question but I have to ask because recently Li-ion powered tools seem to be increasingly cheaper to buy -> which means that their batteries are cheaper too while packing a large punch. That being said, I see that Lowe's/ Home Depot brands sell various 40/60/80V tool brands and these batteries regularly carry 2-4KWh capacities for only $100-200 so I am wondering if these - matched with the correct inverter - could be used as a battery bank because they are all just basic Li-ion batteries right and meant to undergo heavy discharges - because what homeowner actually stops when there is only 2 bars of 4 on the battery indicator? Sure, the chargers that come with them stop charging when they are full but wouldn't a charge controller do the same thing? Right now I am in the midst of expanding my solar 450W to a 950W system and I was looking at alternative battery solutions to go along with the added charging capacity as I don't have a hookup to utility power with the panels (they power a single breaker including my room) and it seemed like I could not find people discussing this other than getting a solar charging system on trucks for charging their tool batteries for a jobsite.

Thanks for the help,
Jayson

[Sunking]

Not compatible, and no real cycle life.

Power Tools use a form of LCO batteries called LiPo. It is a Lithium Cobalt cell with a gel electrolyte to enable them to have very high Power Density and Energy Density or that big punch. LCO cells have a nominal voltage of 3.6 volts which is not compatible with Pb batteries. A 3S LCO is 10.8 volts and 4S is 14.4 volts nominal. Secondly LCO battery cycle life is very low compared to Pb which means extremely expensive.Lastly LCO batteries require a BMS to keep the batteries from Exploding like those used in Hoverboards. Even then they can still explode. .

LFP batteries or Lithium Iron Phosphate is Safe and compatible at 3.2 volts and a direct drop in replacement with Pb batteries. A 4S LFP nominal voltage is exactly the same as Pb of 13.8 volts. They have longer cycle life than NCO, but not as good as Pb. Unfortunately their high cost and shorter cycle life prevents them from being mass marketed. You can buy Chi-Com LFP batteries and many DIY EV builders use them, the downside is they are Chi-Com and do not have good quality. Quality LFP cells are not readily available to the public. Even if they were are to expensive.

Bottom line here the ones you see in power tools are not compatible, and when you factor in cycle life makes them extremely expensive. As you noted $200/Kwr for a 1 year battery. A quality Pb cost $200/Kwh for a 5 year battery. No comparison.

If you need that same big punch, you can have it. Cost the same as Lithium. Use a AGM battery made for UPS. They can deliver high discharge currents of 4C just like Lithium and completely compatible.