It is much easier to go out and buy a replacement for anything that breaks down in your house. Especially the small electronics such as shavers.
For me, I have the tendency to tinker with things before I decide to replace them.
This happens to my 6 years old Panasonic shaver. The battery would not hold a charge for more than 10 minutes. I do have to charge it every time I need to use it which is inconvenient.
So I decided to open it up and replace the batteries myself. I started by removing the bottom screws. Fast forward, I managed to remove the shells that cover the inside parts. 
The batteries that I found were small AA and thus the battery compartment. I had few Energizer rechargeable batteries laying around but they wouldn’t fit inside the battery compartment. So I decided to use AAA batteries that I bought for Ikea. They hold 1000 mili Amps. Much less than the batteries that are inside the shaver, but they will do.
Since I am going to use a smaller batteries, I had to use wires and solder them. Since the batteries were small, so I also needed to use double sided tape to stick them inside the battery compartment.
In the end, I reassembled it and it works great and holds the charge for much longer the 6 years old batteries. Also saved myself a trip to the electric store and 50$!
The Oracle. 