Remove the battery from MacBook Pro and charge it

The positive (+) and negative (-) terminals on the battery are usually the outermost pins. Knowing the specific MacBook model is helpful here.

The MagSafe 1/2 charger outputs 16.5 volts, so you are going to need a charger that supplies that amount.

Now, with all of that said.....

I highly urge caution in attempting to hack a DIY charger for your MacBook Pro battery.

If you don't have the necessary electronics diagnostic/repair skills, this is not something you should be attempting. Besides, there is a more safe and reliable way to diagnose your problems...

You don't need a battery to test out your MacBook.

If you have a MacBook (any model - Pro, Air, etc.) that will not turn on even with the battery disconnected, the problem is with the DC-In board or the logic board itself. And even before you begin this diagnostic journey, you need to make sure that the MagSafe charger you are using is functioning properly. A dead AC adapter won't charge any battery regardless if it's in the laptop or not.