There is a figure in the BP-100 'manual' I received (Rev08 27-03-2017) with the product with some words about second battery protect.
Here's an image of figure 5:
The caution is not sufficient to warn about possible fire when running current thru the BP100 in reverse.
In my case the current was limited to what the battery charger was rated at, 40A. Measured 36A thru BP100 in reverse direction. Limited current probably saved me from a fire. There was a small voltage drop across the BP100 when charging the battery from the charger (I was surprised about this but never figured out why).
Yes, I do consider myself lucky.