I replied in detail on this double-posted thread in another TFF sub-forum. Jason may not be understand he wastes multiple people's time in doing so; therefore, double-posting is frowned upon.
As for jumping a battery with another using jumper cables: Yes, you can do that, but there are risks. If the non-charging battery has a significant internal short because it has failed catastrophically, you may wish you didn't put jumper cables on it. A battery can blow up due to something like this.
The much safer thing to try (pointed in my post on the other thread) is to charge the problem battery with a manual charger for a while. If that doesn't get the voltage up so that the onboard charger can charge it, then that battery should probably be replaced (or at least tested).