For testing, we have a voltmeter with the tips of the cables cut off and soldered to a battery connector. We normally bring one charger per battery, and about seven to the competition (though this is probably a bit overkill). Some major advice: if the battery drops below 10.5 volts, it will get damaged!
I would advise to check the batteries pretty frequently, and make sure they don't go below 11v. Also, when they charge, their max is 14.4v, but it will drop to 13.8v (its max rest charge) afterwards, so don't freak out if they seem to charge and then drop again!