The final compartment is sort of “n” shaped and is located behind the handle and in the middle of the side “P” shaped compartments. In the product listing it shows this compartment as being suitable for “Reader, SD Card and other small objects”, in truth the side “P” shaped compartments are more suitable for housing SD cards. Note I said more suitable, I didn’t say they were suitable.
Like the side “P” shaped compartments the front “n” shaped compartment has 3 protruding ridges, two of which have ridges on the front and back but the middle ridge is only evident on the front edge. Regardless of this the ridge’s are spaced some 2cm apart and so unless you have some 20+ SD cards that require storing simultaneously anything placed within the compartment will simply rattle around.
Due to some protruding ridges in the box lid it is only possible to store 2 AA batteries on the far left and another 2 on the far right of this compartment. If you place any in the bottom corners the lid will not close and while it is possible to place another 4 AA batteries in the centre of this compartment they will be insecure and easily shift to other compartments within the box.
As for AAA batteries the “n” shaped compartment will store a vast amount, far more than I have to hand, you will however need to store a minimum of 20 possibly even 30 at once to ensure they remain upright and to also to prevent the batteries from shifting over into other compartments.