When I disconnect the charger I have seen estimated battery remaining times of anything from 2 hours to 87 hours! However in reality it's more like 45 minutes :(
Do a full battery cycle at least once a month and you won't prevent the catastrophe.
Source: http://batteryuniversity.com/learn/article/how_to_prolong_li...
Storing a battery at 40 degrees C at 100% charge will degrade it by 35% after a year. Drop that to 25 degrees C and it'll be degraded by only 20% after a year. If it was stored at 40% charge instead of 100% charge that drops to only 4% degradation after a year.
My 3.5 year old Asus laptop has still similar battery life as it had when it was new. I always keep it on the charger when I can and sometimes I just shut it down and leave it on the charger overnight too (but this is rare). When I bought it, I have noticed that the battery was never above ~95%, but I have never studied how it works exactly (is it done by HW or by the driver). I have used it with Win7, Win8, Win8.1 and now Win10.
e.g. it's very obvious that Macbooks have multiple different charging regimes, and they use different ones depending on what the laptop's doing and the state of the battery.
"The shorter the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses"
Keeping the battery constantly at stable 60-80% charge is far better than doing full discharges every month.