First of all, you need one of those little 12 volt test lights that look like an icepick with a wire coming out of the handle. With it you can check various points to see where you are losing current. Every hardware store and auto parts store carries them.........about $ 5 or so.

Start at the battery. Take the terminals off both pos and neg and clean them shiny with some emery cloth or sandpaper. Also clean up the terminals on the battery and put the cables back on nice and tight.

Then see what happened. If still no power, go to the starter solenoid that is mounted on the passenger side inner fender panel. With your test light lead clamped to a known good ground, put the probe on the terminal where the pos cable comes in from the battery. Do you have juice there? If so, take the nut off of that post on the solenoid and clean up every wire end that is attached there, and reinstall them nice and tight.

If you still have no power, follow the neg battery cable to where it attaches to the engine block and make sure that end is clean and tight.

If you still have nothing take one end of a jumper cable and clamp it to the negative cable at the battery and put the other end to some part of the body, like a hood hinge. ( You are trying to see if the ground between the engine and body is ok)

Try all that and then let us know what happened. BTW, are you sure both batteries are good and fully charged??

Don