Nearly everything I've pulled apart has had a NiCd in them.
Have tried to rejuvinate them on my multi style recharger, and can't get squat (Rezap charger).
expensive answer, grab a NiMH, needs to be charged first.
Cheap as chips answer, grab the half used alkaline out of your TV remote (put new ones in the remote), then put the alkalines in the solar lights.
They last over a year, probably about as long as the NiCd didn't last, and with the type of use, I've only had one in maybe three dozen leak.