Hi, everyone!

It worked! Thank you all for helping me out in this project. I'd like some tips to choose the right Li ion battery capacity. How do I choose between the options? 1000mAh, 1800mAh, 2000mAh, 8800mAh, 128000mAh?

It all depends on how long and how often you will be running it and how long you need it to work between charges.
Start by calculating the total current in milliamps that the motor and recorder will take and how long it will run each time it is activated.. Multiply the current by the time in seconds.
Have a guess at how many times you need it to run between charges and multiply the answer above by that number.
Add to that the idle current in milliamps that the recorder and any other devices in connected to the cell will use between operations multiplied by the time between charges.
You will then have the total milliampere seconds that will be used between charges.
Divide your final total by 3,600 to convert it into milliampere hours (mAH)..
Select a Li-ion cell that has that capacity in mAH plus a reasonable margin for safety.

 

Get two 3600ma and keep one always charged.

 

We've encountered this problem many times. What we do is use 2 separate 3V battery packs, one for the ISD chip, the other for the motor. Common negative ground on the battery packs and the ISD and motor. The switch connects to the battery packs common negative and supplies negative to both the ISD and motor. One of the positive leads on the battery pack connects to motor, other to ISD. We also put a 1N4148 diode and 10uF cap across the motor.

Why do use the 10uF cap across the motor?

 

For a little extra smoothing of the motor voltage.