On my old laptop, the original battery gave around 1.5 hours life. But I left it plugged in and every now and again, when I would use it on battery (every few months) I noticed the charge was becoming 5 - 10 minutes less each time. Within 12 months it was down to around 20 minutes life. Nowadays, although it has not been used on battery with the original one for some time, when we had a power outage, it struggled to get 15 minutes lol.
I got a battery on eBay and started removing it and putting the old one in as a UPS, keeping the new one charged at about 80% and then leaving it in a cupboard. And guess what, it didnt seem to suffer from rapid degredation like the original one (even though this was a non-OEM cheap eBay battery).
In fact, it is just over 3 years old the second battery and still gives over 40 minutes life. It has only been used on battery approx 50 times and has been stored away from the laptop. The original one had degraded to around 20 minutes life in under a year and had only been used on battery around 10 - 15 times.
So on my new laptop I keep the battery removed and in a cupboard. I charge it to about 80% before I remove it. I run on power 99% of the time you see.