secondary battery is not being charged on 2002 Ford E-350

My E350 Super duty has a secondary non-starting battery I use to run a 12vdc to 120vac generator. I just replaced the secondary battery w/ a new one of the recommended size and the battery does not seem to be getting a charge from the alternator. Are there any basic tests I can do under the hood since the battery is an SOB to drop from the frame to test ?

Asked by for the 2002 Ford E-350
My quick answer is - not really. You really need to see what is happening at that battery itself.

The alternator voltage and amperage output can be determined, though, from under the hood. If insufficient, it could cause your troubles.
Thank you, I will check it out. I'm not sure if there was a fuse in the power distribution box that may be bad, I'm going to check it out also.