New house batteries - not charging?

Recently we replaced the original house batteries with the Trojan gels (purchased from Battery Systems in Seattle WA). We took the old ones out and put the new ones in and everything works - however on the electronics panel, the voltage readings are odd. When driving, the voltage steadily drops. When we turn off the engine, the voltage rises a small amount. This behavior was the exact opposite of the original batteries. We are wondering if they are not getting charged by the alternator. We are only running the fridge. Any ideas on what might be happening here?

Desiree
Westy 109

Desiree,
What are the voltage readings at the panel when the motor is off and while running? You should get (ballpark) 12.5-13.5 while off and 13.6-14.2 while running. Get a voltmeter and check the voltage while off and running at the engine battery as well. If there's a significant difference between the readings at the engine battery and the coach batteries, there's an issue between the alternator and the coach batteries. If the voltage doesn't increase from off to running at either location, it's the alternator. You'll need the 200 AMP version. I got one from Europarts.

Turned out to be the alternator. We managed to coast into a rest stop just before Eugene going south bound. We are at stadium automotive now getting it repaired. Nice folks. Got us in right away and have allowed us to take over their lobby along with our golden retriever.