I'm afraid it isn't easy to join up cells of different types to produce one battery. Adding up the voltages would perhaps produce the 3.7V you're asking for, but the capacity in mAh is difficult to get right and you would probably end up with one of the cells emptying before the others and becoming damaged.
I'd say it's safer to just get the right battery in the first place, but that's more money to lay out unfortunately...
If you have something designed to use 3.7v 650mAH then get the right battery (presumably a Litium Ion / Lithium Polymer cell). It is very important to use the right charging circuit for the battery. There is risk of damage, fire or even explosion if you use the wrong charger.
If you are looking for a battery power solution in general tell us more about your application. You can power a Pi from a variety of different batteries if you use appropriate circuits.