How come the big battery companies don’t use it?

Good question. They don’t want it on the market. If you ruin your battery by running it out of water that is called misuse and neglect and they don’t have to warranty it but guess what, you have to buy another battery. What would happen if they made batteries to last 2 or 3 times longer? That would really hurt their sales and maybe even put some of them out of business. I have seen a battery that had a glass case that was 20 years old and still working. Guess what happened to that company? They are out of business.