Power tools when the power is out.

I am a contractor and have been switching from DeWalt cordless tools to Flex 24v. While sitting in my shop this morning I suddenly remembered an old 10a Rich Solar charge controller I have that has been replaced with a bigger one on my main solar rig. It has 12v and 24v settings. So I hooked up some wires to and older 2.5ah Flex battery I have, and set up a 100watt panel on that charge controller and it charged up perfectly in like an hour. I stuck a fan on it to make sure it didn't go too hard. It was awesome. I know you can charge other power tool batteries this way, but for things like 18v it takes some special equipment, so I thought I'd throw this out there for those of you with 12v or 24v setups like Flex and Kobalt. Yeah, I can just use an inverter and plug in a charger, but thats not as efficient, so bugger you, I thought this was cool.