Don't constantly run on AC. I say maybe old tech, because perhaps charging circuits finally cut off when a full charge is reached. I have a Acer bought in 2007 that actually had a note in the package about removing the battery if running on AC for extended periods. My new Panasonic cordless phones not only have the charge cut-off, but also use two AAA sized NiMH batteries. No more $10-12 a pop for a custom battery pack.

FYI - Michael, information references would be great in articles like this.