Do 9v rechargeable batteries contain charge pump?

[soggybag]

I was helping a friend with an EMG pickup install. We tested it out with a 9V rechargeable battery and there was a high pitched whine. I checked everything and couldn't get rid of it. We switched to a regular 9V and everything was dead quiet. It made me wonder if this rechargeable contains a charge pump?

[Rob Strand]

I was helping a friend with an EMG pickup install. We tested it out with a 9V rechargeable battery and there was a high pitched whine. I checked everything and couldn't get rid of it. We switched to a regular 9V and everything was dead quiet. It made me wonder if this rechargeable contains a charge pump?

I expect so. 

You can see a teardown here,

https://budgetlightforum.com/t/disassembly-of-9v-liion-batteries/43352

and here,

https://www.electroschematics.com/9v-usb-li-ion-battery-teardown/

Your whine test is fairly conclusive.

I also suspect they are not all alike.  Some are likely to produce less noise/whine than others.