Odd question but I recently purchased a laptop to be a dedicated Plex Media Server. However, id rather try not to kill the battery in the process. The laptop has to always be on and to do so it needs to be plugged in. Is their some sort of battery manager that will stop charging then start charging at a certain percentage? Or would that kill the battery faster?
Laptops stop charging automatically. Once they are charged they stay charged till you use them which you never will because it's plugged in. Non-issue.
What kills batteries is being fully charged and stored in a hot environment which is basically what you are doing. If you want to preserve it run it down halfway then pull it and stick it in a drawer. Otherwise just don't worry about it.
Not in most laptops. In all laptops I know of, it'll charge the battery if the SOC (State Of Charge) is at 95% or lower and then charges it back up to 100%. This is so the battery will run a bit cooler by not being constantly slow-charged (slow charging happens at high SOC, can't charge quickly). That same behavior has been happening since the Pentium 3 laptop days and still does the same thing today.
Toshiba, some of them you can set it to just charge up to 80% and then stop. I think it'll start charging again at 79.0% though not 75, still better than being at full charge all the time.
Some other manufactures may offer customization, I wish all did these days. Electric cars do..