I have a dc motor JGY-370 12v 120rpm. I will attach a datasheet that i found about it.
I want to buy a 11,1Volt Li-Po, but i'm not sure about the battery's mAh. At my local website i could choose from 11,1V LiPo batteries, but they have a huge selection from 450mAh to 5000mAh.
It would be the best to draw out the highest torque that the motor can provide.

 

There is no 120 rpm with 12V power supply, only 128 rpm/180 mA, the working range is 6~15V, so if you choose 11.1V should be ok, if you want the motor working more hours then you can choose the one with 5000 mAh.

 

With a 5,000 mAh battery you might get about 27 hours run with a drain of 180 mA. How long of a run do you need between charges ?

 

There is no 120 rpm with 12V power supply, only 128 rpm/180 mA, the working range is 6~15V, so if you choose 11.1V should be ok, if you want the motor working more hours then you can choose the one with 5000 mAh.

So if i understand well it would be good to go with the 450mAh the same as with 5000mAh, the only difference will be the period of time they can go with one charge?

 

So if i understand well it would be good to go with the 450mAh the same as with 5000mAh, the only difference will be the period of time they can go with one charge?

Discharge time DT = 450 mAh/180 mA = 2.5 Hrs
So when you use the 450 mAh battery then the charge time and discharge time will be more quickly.