[C320-list] Charles Charger Inverter Problem

[Crosby Roper]

Hi All,
 
I have Hull # 1054 with the 30 Amp Charles charger-inverter. I went down to the boat the other day to go for a sail and found that the batteries were too low to start the engine. I re-connected the shore power and was able to start the engine without a problem. While out, I ran the engine for a good 40 minutes and the batteries seemed to charge, as I was able to restart the engine several times without any problem. Went down to the boat again yesterday and the same thing.  WHile she is at the slip, I do leave the Fridge running, so I think this is what is draining the battery. The Amp meter on the Charles will initially reads in the 20-25 range, but quickly (Within 10-15 seconds) drops to the 5 range, even though the batteries are low. I took off the face panel and changed the AC and DC fuse, but the problem still exists. 
 
Not sure where to go at this point. I've e-mailed and called the Charles service department today, but have not had a response.  I'm hoping one of you smart engineering types can help. You see, I got a C- in college physics so I couldn't figure this stuff out 30 years ago, and am apparently no smarter now:)
 
Thanks for your help.

Crosby Roper, VMD
Tethys 
San Diego, CA