I just got one of those chargers from ebay, the $11 deal with an extra 1500mah battery, and it works great. Really topped off the battery much better than the phone did - so much so, that 2 1/2 hours after changing batteries my meter still showed 100%. Of course, that was after almost no use (6 mins or so), but still .... much better than when charging via the phone.
I'm just not sure, however, how much I want to be changing batteries. Just not too comfortable taking that door off a lot - it seems so flimsy. But I also don't want to keep fully charged batteries just lying around "just-in-case" and not using them.
I think maybe I'll just rotate every few days instead of every day, and continue to charge on the phone in between rotations.