Since we are on the battery topic, may I know how long does your battery last? Mind sharing how long you get out of your laptop to those who owns 5470? I can't seems to find any proper review on this dell laptop? I would appreciate if you could share me the link if there is any 
- Yes it may have voltage cut off circuit but that circuit can fail (rare but it can happen), and when this happens there is nothing left to safe your battery. Read here for better understanding: http://batteryuniversity.com/learn/article...based_batteries

I used to believe what you believe in the past (based on what I read by others) but last year my phone battery started to fail because I always leave it charging overnight. The next morning woke up, the phone battery is bulging. Battery started to fail after that and since that incident I never leave my devices charging overnight (although sometimes I do forget to remove the charger).

- Yes there is nothing wrong with non-removeable batteries. This is the trend now, they are using polymer battery which is thinner & lighter but performs same as lithium (your vivobook is not using lithium ion but polymer). Manufacturing cost is slightly higher so if you need to replace it, it would cost a bit more. Lifespan on the other hand is same, as long as you follow the guide on how to prolong your lithium battery there is nothing to worry about. I am also using non-removable battery in my asus zenbook & it is still performing in good condition after a year plus.