This would certainly be useful. My dell Studio 1737 laptop reports a 5,200mWh battery, but it actually has a 56,000mWh 6 cell battery. Battery life is crap though, such a high power machine only lasts 1:10 to 1:30 even on the most economical settings

I think if you're going to do the

"Add the possibility to set the Designed Capacity manually"
http://feedback.osirisdevelopment.com/pages/4284-batterybar/suggestions/94531-add-the-possibility-to-set-the-designed-capacity-manually

you should seriously take mWh vs mAh into consideration (either with a clear note, on or linked from the preferences page, of which is which and how to calculate if you don't have the right one; or simply with a radio box for which was entered) as a lot of people may be thinking their is reporting wrong because they didn't notice or don't understand the difference between mAh and mWh. If people were to set theirs to a mAh value in a mWh field without realising it, it will cause you a lot of headaches with people complaining of a bug which isn't there. My laptop batteries and the listings for spares I can find online are only written in mAh for both my laptops.

I didn't articulate my point very well, I hope you get what I mean.