What are the disadvantages of Sanyo Eneloop NiMH batteries?

[S.S.]

besides the fact that the initial cost is expensive?

[E. F. Hutton]

Nothing really. Why pay extra for an already charged rechargeable?
After that you run into the voltage level issues of all NiMH cells versus single use chemistry cells, 1.25V versus 1.5V which will affect some devices. They should be disposed of properly as with any rechargeable cell.
Other brands of NiMH cells offer higher capacity.

[DarkMist]

One apparent disadvantage of the Eneloops over normal NiMH cells is lower capacity. For the AA size, Sanyo claims a capacity of 2000mAh. Normal NiMH AAs are available with capacities of up to 2700mAh nowadays, but when you consider self-discharge rate, such NiMH cells stored for about 30 days will drop to 2000mAh.

[E. F. Hutton]

Nothing really. Why pay extra for an already charged rechargeable?
After that you run into the voltage level issues of all NiMH cells versus single use chemistry cells, 1.25V versus 1.5V which will affect some devices. They should be disposed of properly as with any rechargeable cell.
Other brands of NiMH cells offer higher capacity.