Tablet I bought for wall mount HA control has smart charging as an option, it says it will keep battery between 40% and 60%. Would that be good enough?
Or should I opt to connect the tablet to a smart plug where I can turn it on to say charge to 80, then turn off and let run on tablet battery until its down to 20, then turn plug on, etc etc.
Either will do.
If I were you, I would pick the built-in, and test & verify, while still leave some space at the plug location - in case someday somehow I had to use the other one for whatever reason(s).
The smart plug will also use energy and is extra costs.I would go for the build in smart charging. Probably more energy efficient and a cheaper total solution.