If that fan keeps running, yes, you may just have a big load, but very often the batteries are already mostly used up. They are the big load and may not take or hold a good charge. Running the battery/batteries down to or below 11.9/12 volts takes a toll.
If these batteries were in the rig on a lot for length of time they may already be toast. Sales people are known to run em dead before charging and then not necessarily charging them well, at that.
In Sunny So Cal /w
Now in 2005 Holiday Rambler Ambassador DP and The Hot Air Balloon RESTLESS
NO MORE Tricked out
2017 Sandstorm 250 T.H.