Its tough to measure the condition of a battery pack without the proper equipment that can measure and calculate the charge values. A fully charged battery pack should read somewhere around 18V. You have to measure it after it sits for a few hours following a charge cycle, so that you are getting the true voltage and not the residual voltage that is only there due to the chemical activity of the charge and will dissipate.
If you have a multimeter, you can measure the voltage of the fully charged battery. Then attach the solenoid to the battery pack with the multimeter already attached. Once the voltage settles to a readable value after a second, read it and disconnect. It should only be on for a second to prevent heating of the solenoid. If the voltage dips significantly, you have a bad pack. If it stays relatively constant, the pack is good. The voltage shouldn't dip below 16.8v. The starting no load will be higher than that, usually greater than 18v. Make sure you measure the starting value after the pack has been off the charger for a few hours or it will not be a true representation of the steady full battery level.
If your batteries have been sitting dead for a significant amount of time, there is a real possibility that they are bad. Dead cells develop deposits on the electrodes which impede the ability of the cell to deliver a current to the load or receive current from a charger. Once these deposits are present, they are hard, if not impossible, to remove.
Except for the Automag in front, its usually the man behind the equipment that counts.