I've also noticed that the chargers that will stop at 80% are very hard to find currently. A workaround is to invest the time to figure out the rate at which your charger fills your battery by stopping it every half hour or even 15 min, and reading the voltage out of the charge port, (with the charger removed) with a voltmeter. There are lots of internet sites with voltage/percentage charts for various voltage batteries. Then you can make a graph of the voltage/%age on the vertical axis and time charging across the horizontal.
This graph will allow you to estimate very accurately the time required to go from whatever state of charge you are starting with to whatever %age you want. Then with a hardware store timer outlet, you can set the timer to stop the charge at that amount of time. My 48v 17ah goes from 45v to 51.7v in about 3hrs and 15min on the charger that came with it.