Update: Testing/development is complete and production boards have been ordered. Estimated arrival is about 2.5 weeks. I will be working on the website during this time.
For those of you who want to build one as soon as the board becomes available, if you order the batteries online (such as eBay) the shipping time may be 2 weeks or more, so you may want to start looking now. You need two 3.7V 600mAH lithium-ion polymer cells (Walkera HM-4G6-Z-37, HM-4#6-Z-34 or equivalent, for Walkera 4#3, 4#6, 4G3, 4G6 RC helicopters). These are commonly available from RC hobby retailers and online. The two cells fit perfectly in the Mini³ Hammond enclosure, where the 9V NiMH battery occupied. The size of the battery (each) is about 42mm x 25mm x 8mm.
Please do not substitute with other batteries even if they fit. The charging circuit parameters are tailored for the specified batteries.
I have a very small number of these batteries on hand, when the boards arrive you may ask me to add two of these batteries to your order, but it's on a first-come, first-served basis and may run out quickly.