Since the all-day laptop battery is still a rarity, it's essential to carry a spare if you want to keep working on the move. The Ansmann Portable Power Pack for Notebooks (£175 inc. VAT) claims to double your uptime, but the reality is a little less impressive.
More than twice the size of most laptop batteries, mobility is limited. Also, its high price puts it in line with the most expensive official batteries that can be bought with a laptop.
In day-to-day use, the Power Pack ran our test machine for 160 minutes. Since the laptop's original battery was half the size, half the price and ran for 201 minutes, this was disappointing.
If you have no alternative, then this may suit your needs, but for most people its just not worth the money.