What I do...
You can actually charge using any of those connectors. Yes, use the large black type 3 pin with 2 wires for going into your 9x to power it. Better yet make an adapter out of the original 3 pin plastic battery holder and add a matching servo type connector you can plug the black one into.
Be very careful with polarity when you wire it. Just cut the black tab off or use a Futaba type servo connector. Then you can also charge with it if you decide to.
Why I don't plug the black connector in my 9x directly even though it fits and is polarized OK is because it sticks out of the 9x connector a lot and can be in the way or come lose.
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Next, I replace the 2 pin white plug with an orange JST type connector again keeping the normal polarity used for + and - . I then can charge using that connector and don't have to unplug the black one the adapter for the 9x. Finally you'll want to use the white 4 wire connector for balance charging. Some chargers actually use only this connector for charging but most require it and one set of red and black wires on the other connectors. I usually don't charge my life battery in my tx but what I do is open the battery box and pull the battery out far enough to get it away from the tx. I then use the JST connector I added and the balance connector to charge or mostly just the JST. You can remove the battery by unplugging the black connector and leaving the adapter in your 9x and it's any of the connector combinations that work for you for even a safety charge setup. I avoid unplugging and re-pluging
The connector that goes into the actual 9x board to avoid wearing out or damaging the connector over time.
Charging with the battery in your 9x is the least safest even though the life has a less chance of fire, it could puff and do damage to the case so I don't do it!
Unplugging from your tx is the safest with at least pulling the life out of the case connected is next safest.
DON'T even think about using the life's 2 pin white plug into your 9x 3 pin connector! The 9x 3 pin is + on the center pin and -(ground) on both outside pins ( connected on the circuit board).
Of you plug the 2 pin shifted to one side of center the polarity is IK, shifted to the other side and you've reversed polarity and you'll fry your 9x when the switch is turned ON!
It's done all the time and it's a ticking time bomb. I've repaired several for friends that fried their radios a few days after being brand new after using the 2 pin white plug.
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