'94 Ford Taurus SHO stick, daily driver for about 15 years: I replaced the battery about the middle of every Texas summer- yeah, heat kills, but still, in spite of buying 60+ month batteries. Had a vampirism problem with a faulty alarm that took out two in one year, but other than that, eating batteries was just the price I paid for the enjoyment that car gave me.
Strangely enough, I am using an ACER notebook now that I keep plugged in probably 80% of the time that I use it (and, yes, I know better, I just don't care enough to change). The battery life is down only 20% over when I bought it close to a year ago. I am thinking that the BIOS might be limiting the battery charge to 80% to slow down the destruction of the battery, because I didn't get the expected life out of the battery compared to my previous notebook at the start, but at the one year mark and same usage pattern, this Acer is doing much, much better.