The example I saw with a really low battery bank (two 6s) still had enough volts to allow the smart charger to operate. That meant the battery was over 4 or 6 volts whatever the charger spec on that is.
( If lower voltage at first, you need a non-smart charger (like jumper cables) to get past 4-6 volts first, then cut in the smart charger and it will do its routine.)
The smart charger (a Vector A model) was set at 14.6 and battery voltage slowly climbed while amps did too, until it got to the "mid-voltages" when things went to "normal" and the batteries did ok after that.
Still not sure how you can tell it is not going to work (unless the battery gets hot) unless you try it. ?????