One other thing just came to mind. If the batteries donn't have a matched load, when it comes time to recharge, you could overcharge on pack and undercharge the other as you will work on the average of the two. This would be a problem with either a parallel or series setup. If you use the series setup, it would be best to discharge each pack on the RX side them plug them together in series for a full charge on the TX side

The simplest answer though is to charge one the the Accucycle and the other with the wall wart from your TX.

Don