For many years, my "beach amp" had its two series strings of 6 AA Ni-Cads connected in parallel without any problems. I used a National Semi stereo amp IC (discontinued now) bridged for each channel and got about 6W per channel into 4 ohm speakers all day long.
After being on trickle-charge for about 20 years, every single cell ended its life shorted.
The rechargable electric screwdriver I inherited must have been charging for at least 25 years and still works fine. It doesn't have paralleled battery cells.