If you examine the typical usage, or expected usage scenario, you actually can determine the general protocol for how to treat your battery.
In general, a laptop owner will plug in their laptop if they are near an outlet, and use it while it is connected to a wall outlet for the duration of their session. They do not want to be bothered with removing their battery, or connecting/disconnecting from the wall outlet at regular intervals. In more extreme cases, if a laptop battery has ever proven to have an issue with this type of usage (getting excessively hot and/or exploding while the laptop was plugged in) it was recalled as being defective. So, this tells you first of all, that allowing the battery to maintain a full charge for an unlimited amount of time is not a bad thing for maintaining a healthy battery.
We move on to looking at general laptop usage off a power grid. Most people actually don't open their laptop and in a single session drain their battery until the laptop shuts off. Most people actually use their laptop on the battery for a few minutes, and then turn it off. They will use it a few more times for sessions of varying length, get the warning that the battery is low, and then plug it in to charge. This is not to say that some people don't use their laptops in a single session until that warning. Of course some do. Just that most don't. Almost everyone will see that warning of a low battery... a 15% to 5% remaining charge left warning before they seek a power outlet. Which means that a large number of laptop users... one could say a Majority of laptop users will use their laptops on battery until it is drained before they charge it again.
Here is what most people miss. It's not so much the temperature of the battery that will reduce it's life. It is the number of charge cycles. The more times the battery is charged, the shorter the amount of time it will provide a full charge for. By charge cycles, I don't mean the number of times it has received a micro-charge... sitting there topping off constantly. I mean, the number of times it has been drained significantly, and then recharged.
For example. I have a 2004 Toshiba Satellite A75 that is a power hungry monster (120 watt adapter). Two fans, 3.33ghz P4 HT processor. So, with the battery that came with the unit, I would see around 2 to 2.5 hours of usability on the battery when new. I still have the original battery, and I can get just under 2 hours of use out of it. Why, after 8 years does this battery still function relatively well? Because the laptop BARELY ever gets used on the battery. The battery sits in the laptop, and the laptop sits on the counter plugged in all the time.
If you have an actual UPS.. a battery backup system, it will retain the ability to run a system on battery for a longer period of time if you don't actually end up using it.... as opposed to if you have to use it every week due to power outages. If you have a home alarm system that has a battery to maintain it, that battery will last 4-5 years if you don't have frequent power outages, but might only last 2 years if you have a large number of storms that kill power for hours at a time. It's all about the charge cycles.
If you want to extend the battery life... meaning if you want to avoid having to go out and purchase a new battery, then actually not using the battery is the way to go. Leaving it in the laptop and just not using it on battery power will give you the longest usability life span possible. That's not entirely feasible though if you want or need to use the laptop on battery power.
Here is a suggestion. Purchase a second battery, and purchase an external battery charger like this one. Why? Depending on the external battery charger, it will either spend less time charging while on the external charger (which will mean it will be getting warmer for a shorter period of time) or if it is a trickle-type charger, it won't get as warm while charging. Then, you can use the second battery while you are charging the first. Should you be concerned with the temperature of the battery while it is charging? No. But, this solution would alleviate those concerns.
Otherwise, just use the laptop as you have described.
