I got to an item on my to do list today and just had to share a Mustachian solution as my first post.
We have a Verizon internet/phone connection box in our garage with a battery backup. For months it has been beeping at us to replace the battery. This is about a 10lb 7ah, 12v battery that provides continuity of service in case of power outage. I finally opened the box, removed the battery and a virtual lightbulb went off in my head - ‘Hey, this looks really similar to a scooter battery!” About 6 months ago I refurbished a razor scooter with 2 new batteries and still had the old ones laying around. Sure enough, same size.
I took the first scooter battery, ground off the solder on the contactors, plugged it in and VOILA, no more beeping; just a happy green light.
Zero $ spent, way less time than going to the store, and one less battery needing to be produced in the world!