Makita recently announced the DC18SF Rapid Optimum charger, which accepts up to four batteries at a time.
Details are sketchy, but the device appears to charge all of the batteries at once – as opposed to sequentially, like the Milwaukee Six Pack charger does.
The DC18SF should be a boon to anyone who owns a lot of Makita batteries. According to the manufacturer the device can charge two full-size batteries in 60 minutes and four full-size batteries in 120 minutes. Compact batteries can be charged in half that amount of time. The charger monitors each battery and controls the current, voltage, and temperature for faster charging and longer life. Charge indicators display the charging status.
Suggested retail is $169 though this tool can likely be found for less on the web.