Just disconnect the chips at the top of the phone and connect them again. That did it for me.
I bought the Panasonic Eneloop AAA batteries as somebody suggested. I didn't want to solder as I have no experience and did not want to damage anything. Besides what would one do after the batteries go bad and you have to replace them again. The metal wires are already damaged the first time after they get disconnected.
I used tape as somebody else suggested. Just tiny slices of tape to attach the wires to the batteries and it seems like all is working. My unit is currently charging and right after I will test if it operates correctly.
I would say that the panasonic batteries are longer so they don't fit perfectly but it's possible to fit them if you are careful. Just remember don't go crazy on the tape and straighten the parts of the wires that connect to the batteries so they don't take extra space!