When I see the words "REMOVED BATTERY" I always have to ask is the Battery Installed correctly. It is so easy to mix up the cables... What I do is find the word 'NEG" or the Symbol '-' stamped into the battery case and make sure this is the cable that goes to FRAME GROUND close to the battery...
In the RV TRAILER WORLD the battery cable colors are BLACK for Positive and WHITE for Negative... In the AUTOMOTIVE WORLD that all of us are very use to working with is RED is Positive and BLACK is NEGATIVE...
Also anything that has a in-line fuse etc most often is connected to the POSITIVE terminals...
If the battery has been REVERSED CONNECTED it will blow the REVERSE POLARITY fuses located in the CONVERTER/CHARGER unit... Looks for those as well...
Roy Ken