You may only achieve half the stated battery life on many laptops as some laptop manufacturers greatly overstate it, Which? tests find:
"When it comes to laptops, battery life can be a key buying decision. But Which? has discovered that the battery life claimed by laptop manufacturers rarely lives up to reality, with our tests finding it often falls drastically short.
Which? testing has shown that almost all laptop manufacturers overstate their battery claims. In some cases, the battery life estimates were double what we achieved in our lab testing."