So, you are right, I forgot to say regular batteries can only be charged with an external charger, unless you integrate them in an old battery pack as you did.
At first, I saw Barrier's message (You don't need...use
regular NiMH...).
So I ran to a shop and bought 4x NiMH AA, then
I realized that was a wrong advice!
At once, I took my cutter, my soldering station
and my patience. I opened it and exchanged batteries
cells. The most delicate was to pull back stuck
parts without break them.
No I have a new pack NiMH 1800mAh for 18$.
Thanks to mister Barrier for his mistake. :-)