That photo shows the black wire soldered to the Bat-, and the red wire is right by the Bat+, which looks to have excess solder on it. My bet, that's where it goes. My advice, check with the manufacturer whether that is correct then solder away.
Edit: (10 AM EDT) I needed more coffee this morning. I saw the above photo and thought it was from the OP, until looking at it again after my third cup and realizing one,
@sawlight was not the OP, and two the pic sawlight posted was a DIY shot which was even labeled as the Bat+ wire. So, basically, nevermind........