Ruivar,
There are quite a few batteries sold on Ebay as Beocom 6000 batteries which look the same, fit into the phone and are the correct voltage of 3.6 volts but still do not work.
The reason is that there charge current is different (higher), so when they are put on charge, they do not actually charge.
Have a look at the batteries in your phones and they should say on them SANYO Ni-Mh model 3HR-AAAU 3.6v and normally have a yellow covering. If that is not the case, then order some new batteries of the correct type.