The best part is those older toys with low batteries would have an extra creep to the voice because of the low voltage. We had one that sounded absolutely possessed by a devil. It was truly terrifying to hear that in the middle of the night :-D
This effect still happens with cheap battery-powered cat toys that chirp. Some are rechargeable... others are not, and keep squawking pixelated noises of various pitches for years on end. Ask me how I know.
Good for circuit bending! I miss the times when just a resistor or bat voltage controlled the chips clock cycle without insta-crash
Doubly so if they were motorized toys, so when the motors kicked in, the battery voltage would droop and make the pitch shift even more...
It is not uncommon to for some guitarists to use partially depleted batteries to power certain effect pedals, especially fuzz pedals. People can get particular about tracking down specific brands of carbon-zinc type batteries that are perceived to have preferred discharge characteristics. And there are “battery sag simulator” pedals.
https://danelectro.com/product/1960s-vintage-battery/
https://jhspedals.info/products/volture?srsltid=AU7gw4VF4W_4...