This will show you how to replace the internal battery on your Sonicare Elite 7300. After having my 2nd one die on me within 3 yrs I figured out how to rip it apart and fix it.
Step 1: Disassembly
The first part of disassembling the elite 7300 is removing the small trapezoidal rubber bumper at the top back of the unit. This piece has two small clips which holds the internal components inside of the casing. Next, slide the main screw ring (upper left) off of a brush head. Twist the screw ring down onto the handle all the way and pull the internal components straight out.
Step 2: Remove Battery
On the PCB there are two solder points which hold the battery in place (red arrows). Use some de-soldering braid and a soldering iron to free the legs holding in the battery and which also provide the electrical contact between the battery and PCB.
Step 3: Battery Removed
This is what the battery looks like removed.
Step 4: Prepare for New Battery
Solder a wire to each of the pads shown in step 2 and route them through the plastic to the back of the PCB so we can use them to form the connection to the battery.
Step 5: Battery In
Get your 4/5A cell the OEM was NiCd but I used NiMH which should have longer life.
Scratch up the positive and negative terminals of the battery with a hobby knife so that way solder will stick to it. Use a low watt soldering iron (you do not want to apply too much heat to the battery) to solder the correct wires to the positive and negative terminals. Stuff the battery back in the compartment and tuck the wires in so we can reassemble.
Step 6: Put It Back Together
Slide the internal part back into the handle casing. You might need to apply a little force to get it to click in all the way. Replace the small trapezoidal rubber stopper and you are done! Enjoy your Sonicare which will now hold a charge and function like it did when it was new. Charge it up and away you go.
Recycle the old NiCd cell.