The 650 mA chargers will charge your extended battery, they'll just take longer. That may be OK if you're charging it overnight, say, to carry the next day.
The phone will apparently draw up to 800mA when charging, so it would charge a little faster in the phone, but not a lot. The 650 mA charger would charge a totally discharged battery in about 6 1/2 hours. Charging in the phone would take about 5 1/2. Remember, those estimates are for a totally dead battery. If you start recharging with about 25% of capacity left, the times will be shorter.