looking up video's how to change the batteries, I could but I wouldn't bother, you could lose or break parts and you might not be able to get a matching battery as it seems braun dont do this model anymore.
Buy a toothbrush that takes AA or AAA batteries then buy a charger, usually includes set of four batteries, use them in the toothbrush two using two on charge.(Make sure the charger has two selections one to charge 2 one to charge 4.

Just weigh up the cost of above against buying a new elec (built in battery ) tootbrush.

bobuk
September 2018