Gregg Keizer at Computer World has done a little detective work on the battery life of Microsoft’s Surface tablets and has found that it may be lacking compared with competitors. CW‘s rough estimates, which were calculated by “by comparing their watt-hour ratings with existing products that have made between-charges claims,” found that the Windows RT Surface may have battery power in the 7.5-hour range, or around two-and-a-half hours less than the advertised battery life of the new iPad; Keizer says that the Windows RT Surface tablet has a listed battery power of 31.4Wh, more than 10 watt-hours less than the 42.5Wh battery in the new iPad. Keizer also spoke with iFixit CEO Kyle Wiens, who “cautioned against reading too much into the estimates” since “there are simply too many unknowns that will determine Surface battery life.”