I've never tried the lowest brightness level for an entire charging period (my eyes just aren't that good!), and without network, I don't have much use for any computer-- that's what I get for heading up a website for a living
But I'd estimate that you could get an extra 45 minutes that way.
Convertibles are larger and do weigh more, even if money isn't an issue. That said, if I were looking at bang for the buck convertibles, the HP TouchSmart TM2 is super (gloss screen that's not IPS being the only drawback), and the Lenovo X220 Tablet is one of my top choices for more money. Thanks to Lenovo's continuing discounts and coupons, you actually get a lot of machine for the money. The X220 has strong battery life and an Ethernet jack .
-------------------- Lisa Gade Editor in Chief, MobileTechReview