I notice that the 9900 has a slightly different battery compared to the 9700 and 9000 series. The new JM1 battery is obviously thinner and has a bit less capacity than the old M-S1, but is very close to the same length and width, and the contacts are almost in the same place.

Would it be safe to charge a JM1 in a battery charger we bought for M-S1 batteries? Has anyone tried this? Note that I'm talking about a standalone battery charger, not something that plugs into the phone.

I assume the phone chargers are interchangeable apart from the micro/mini USB issue.