Thanks for all the replies. I've never noticed a defrost switch on the fridge. I've looked. Once i get the cover off the trailer i will check the wfco model. I do want to pick up a DC clamp-on ammeter. Still not sure if the old grp 27 is good. It's been sitting in the garage idle for a couple years. I have put the stand alone charger on it a few times. If it is good, i would take it as a back-up and not parallel it. I may just take it as a return for the core charge and pick up a 2nd grp 31