How to replace the internal 1.2v Ni-Mh battery.
NiMh 1.2v Batt (simil).... https://www.ebay.it/itm/BATTERIA-RICA...
Notice that original battery is shorten than the new one, you will have to cut some small plastics on the battery socket to allow the installation of the new (and longer) battery, it is too easy.