This is my Braun 5510 shaver with rechargeable batteries. The batteries no longer hold a charge. It is possible to use the shaver with the AC cord normally used for charging. I wanted to replace the NiCad AA batteries with new cells.
Step 1: Opening the case
The first problem is how to open the case of the shaver. This graphic from the shaver's manual gives some description. But, these instructions assume you will no longer use the shaver after opening to remove the old batteries for recycling. The seal is green as shown. Use a larger coin to push and break the seal. Then rotate the round fitting where the cord attaches counterclockwise about 45 degrees. Rotating this cord jack fitting required considerable force. I had to grasp a US quarter dollar with a pair of pliers to apply enough force.
Step 2: More on opening the case
In MS Paint I added some colored lines to illustrate the steps in opening the case. As described in the previous step, rotate the fitting around the charging cord jack counterclockwise (red arrow). There is an end cap on the case as shown by the yellow lines. When the fitting around the cord jack has been rotated, the end cap slides off (yellow arrows). Then the major portion of the case slides away from the innner workings of the shaver (green arrows).
The inner carcase of the shaver is not shown here, but it is a clamshell. Pry it open only as far as needed at the end of the shaver shown in the photo. Slide the inner case for the circuit board and motor out of the shaver.
Step 3: Inner case catches
The inner case around the circuit board is an upper piece of translucent plastic. The lower piece is black plastic. Four snaps hold the two pieces together. Gently pry each off of its hook. The graphic illustrates the hook catches.