Why the concern?

I feel like The Internet has this urban myth that says keeping a charged battery plugged in all the time will eventually cause it to explode and burn your house down, guaranteed.

I get that keeping a battery at 100% charge is not great for it in terms of longevity (ability to hold a charge). And it's obvious that heating the battery up by running the laptop at full tilt inside a backpack or something will turn it into a spicy pillow.

But I struggle to imagine the failure mode that reliably shows up when keeping the laptop powered on 24x7 that is never a problem for 8-16 hours of continuous use while plugged in (a very typical work day for my laptops).

I usually disconnect the battery and just power them via USB-C. The battery on these old broken laptops is usually toast anyway...

You can just limit maximum charge (using something like aldente), then replace the battery every 4 years if you need extra peace of mind.

Batteries degrade much faster when fully cycled repeatedly, and even then just about any laptop battery can easily make it 6+ years with low-to-zero risk of failure.

Most old PC laptops have external batteries you can detach by pulling out on a springloaded tab. Even MacBooks are possible to run without the battery, but it requires some NVRAM trickery IIRC.

Maybe put it on a timer, or have the laptop control its own outlet.