Lowes sells a clamp on amp meter that measures both AC and DC amps for about $80. If you get the $40 one, you will be disapointed, as it will not read DC amperage.
Then you can clamp the meter over one of the wires, and measure the DC amps. It will also read DC volts, and if you are charging at say 14.4 volts, it will be putting out the max amps. A full battery resting is 12.8 volts. Most chargers sit at 13.3 volts once the battery is full, and it has slowed down on the charge amperage. It should stay at the 14.4 volts for either 4 hours or until it is only putting out say 25 amps, then it will automatically drop back to the resting voltage around 13.3 volts.
Good luck!
Fred.
