I have built a little medical assistive device using the raspberry pi 3, I wanted to attach it to a backpack and test it in real life situations.
I don't have much money to purchase much things but I did get 5 free Lithion Ion batteries from a friend they say 36Wh and 7.4v,
How would I go about using these for my raspberry pi 3? (and if suggested not why?)
You could run the Pi on 1 battery - if they are in good order it would run for upwards of 7 hours. You will need a switch mode power converter (similar to UBEC) to drop to 5V. These are available inexpensively on eBay.
DO NOT attempt to run the batteries in parallel. This requires additional circuitry to balance loads, although you could use 2 in series with a suitable power converter.
