Radio Shack sells a repair kit with the Tamiya connectors, in fact two and the only difference is the wire guage. One is marketed for 7.2 volts the other for 9.6v. Less than $4 for either. If you think the problem is the lenghth and guage of the attached wires, just shorten them and use the RS repair kit to make the length you want.
Can't help with them dieing if they ran too low. If you have a voltmeter check the wires as close to the batteries as possible to see if they have a charge, then check at the connector to see if the voltage is lower or 0 which would indicate a break.