Using a plug-in timer to extend the lifespan of a laptop battery
Do you actually need to run the laptop not plugged in?  Is it an option to simply plug it in when you're using it or have the timer run for that period of time?
A 12 hour charge is likely to at least somewhat overcharge the battery, so you may wish to run it dead and see how long a full charge actually takes.  My laptop charges fully in about 1 hr and 45 minutes and it's nothing special.  I would think a modern laptop would only apply a periodic topping charge to a fully charged battery and that leaving it plugged in would produce few issues, but if it is damaging itself, yes, limiting overcharge time will increase battery life somewhat.  Outdoor block heater timers come to mind.  They're about $20 where I live and you can control the power cycle over the full day in 15 minute increments by flipping little tabs.