The Syncro is an electric razor produced by Braun. It features a self-cleaning dock system and runs on rechargeable batteries. After years of use, you may find that the batteries no longer hold a charge; this is when it is time to change them out.
Purchase a replacement circuit board. At a site like "Buy It Now" or "The Parts Biz," order a replacement circuit board for the Braun Syncro. The batteries are attached to the circuit board. Order the model that is compatible with Braun Syncro model numbers 7505, 7510, 7515, 7515 and 7520.
Open the Syncro. Using a flathead screwdriver, pry off the bottom of the shaver. There should be a small groove to fit the screwdriver into. Carefully pry open the bottom. Popping this part off will reveal two tabs holding the sides of the shaver in place. Carefully lift these up and pull the sides off. This will reveal four screws. Remove the screws to take off the entire backing.
Carefully remove the circuit board. The board also contains the batteries, which are permanently attached. Dispose of the batteries and circuit board in a responsible manner, at a recycling centre.
Put in the new circuit board. Taking care not to damage any of the small parts, slide the circuit board into place in the base of the Syncro.
Put the Syncro back together. Attach the backing with the screws, followed by the sides. Then put the bottom back on.