Built-in laptop batteries: buyer beware

A worrying trend has hit recent ranges of laptops: the battery is built in, necessitating a return to the fatory in the event of a change being necessary. There are several culpits. The one that sticks to mind is Sony. The new laptops are sleek, thin and nicely streamlined. The use of ultra thin polymer batteries helps, as it enables the battery to be spread over the whole surface of the base. Great, until the time comes to replace the battery.
In my expeirence, typical battery lifetime is around three years. So, this effectively means that the ultra sleek, and expensive, laptops can now be expected to last just three years.