Hi Peter
Sorry I can not take a photo as it's now back in use.
They are square and white, you will find them under the plastic cover where the fan is.
Undo the top board and lift it back and you will see the plastic covering, gently lift the two
battery like things and remove the one screw from the plastic cover and if you have the back facing you
in the left hand corner there's a clip what locks it to the board gently move over and lift it, then on the right on the front side
of the cover there another clip do the same to that and then you can lift the cover out of the way.
I then removed them from the top of the board by rocking them back and forth until they broke off. the numbers again
are C 215 C216 C415 and C416 they are easys to find just look for the numbers and as I said the sound is so much better.
Over the weekend I'm going to do the same with my 5500
If you are unsure I'll take it apart again and take a photo but it's really not difficult.
It's like having a new system.
Regards Henry