Charging Chassis batteries

[vettehead]

When I start our coach it is a bit slow turning the engine over. Battery voltage drops to 7-9 v while starting. I have load tested both battery's, and they are good. I keep it pluged to shore power. Inverter is set for "Float Charge". Moniter shows charge to house battery.
I pushed the Booster switch but it dosesn't help during cranking. Anyone know of the location of the solenoid that connects the two sets of batteries? Is it the ISO solenoid in the rear run box? It hum's all the time. I don't hear a noticable click when I push the boost button. Maybe get the BOH out there tomorrow to see if she can hear it.
Coach is a 2006 Exec with ISX.
Any help will be apprecated.

[Mike Canter]

It is one of the small solenoids on the right side of the rear run box. One of the small (Ford like like starter solenoid) is for the salesman switch and the other is the battery boost. If you have a very large solenoid on the middle left center then that is the Big Boy for the B.I.R.D. battery charging. The primary charge when on shore power or the generator is to charge the house batteries until they reach 13.2 volts then the Big Boy Solenoid energizes and it will charge the chassis batteries. If the house batteries do not get up to 13.2 volts for some reason then your chassis batteries will only be charged through the alternator. Since you have tested the chassis batteries and the battery boost makes no difference then I would suspect the starter to be bad and dragging.

[HTFireMedic]

Have you load tested your starter? One of our fire trucks did the same thing and the starter was bad.