I think I remember you saying you had to store the trailer remotely.
If so were the batteries with you for storage so they could be reinstalled fully charged when you went on a trip?
If they were stored with the trailer, and it was not plugged in to shore power, you likely left with discharged batteries.
Also, why did you shorten your trip? You could have recharged the batteries while camping with a simple set of jumper cables connected to your tow vehicle for a half hour or so, morning and evening. It wouldn't fully charge them, but it would have boosted them enough to continue your stay.