Point 1 in the operating instructions: "To reduce the risk of damage, we recommend using only rechargeable Ni-MH batteries from Panasonic". If you were to use NiMHs from other manufacturers anyway, it would also work with them. But that is purely hypothetical.

So 4x AA can be charged at the same time. I don't know how many AAA batteries can be charged, but I think 4x AAA or 2xAA+2xAAA.