[Jim B]

I would do a conventional cranking voltage amperage draw test as well as a battery load test (disconnect the battery from the vehicle cables when performing the load test and be sure to get the normal specs from the specific starter and battery manufacturer !!!) Also do a static draw test to make sure you don't have a static drain. Those two should identify the problem area if it is in the battery/cable/starter chain. Also don't overlook an internal broken battery post connection though with two batteries that's probably not the problem. There's gotta be easy access to a VAT 40 type tester.