Most of the old rechargeable aa or aaa batteries were NiCd, which would be 1.2V vs the 1.5 you get from alkaline. I believe the voltage drops off more slowly th

Most of the old rechargeable aa or aaa batteries were NiCd, which would be 1.2V vs the 1.5 you get from alkaline. I believe the voltage drops off more slowly than alkaline, but since the starting voltage is lower some devices just can't handle it. We had a set of cb radios when I was a kid, they had 12 aa battery spaces but two "blanks" installed. You used the blanks and 10 batteries for alkaline, but removed the blanks and installed 12 if using rechargeable to bring the voltage to an acceptable level.