How do I charge this battery?
If the battery's capacity is 650mAh then in a perfect world (and with a discharged battery) you'd need to charge it for 6.5 hours with 100mA.

But, unfortunately it's not a perfect world and you'll need to charge it maybe ten hours at 100mA.

Why don't you look-up the data sheet of the battery and see what it recommends. It might let you charge it at 650mA then you'll need something between an hour and 2 hours to fully charge it.

READ THE DATA SHEET ON THE BATTERY