I checked the thread above - quite a reading. Thanks for the link and your recommendations.
Most likely I'll try to do several times re-balancing and see if it helps. My personal experience with NIMH batteries (for consumer electronics) - if charge level drops - it's not fully recoverable. Maybe you can improve it by 5-10% but it'll go back to lower state quite soon. And since I do not have a garage - only parking spot - it's not an option for me. It would be OK to do charging once - just to bring battery to life. But constantly reconditioning the battery with low chances of success would be a bit of challenge for me. Will update thread with new data points when available.

 

One more data point. Looks like it's related to temperature. Today it was colder 45F at night and I had stall conditions again. This time I was able to capture battery parameters an I think you were correct suspecting failing battery element.
Look at the 6:95 time. There is a huge spike in DEL_MOV_V - up to 2.2V with almost 0 Trac_M_AMP current. Strange behavior. But most likely this is the root cause.
Second attempt was with fault again. Same spike to 2.3V.
Third attempt to start engine was OK. Battery temperature increased to 15deg C. No jump in the DEL_MOD_V when current is small. Will try to find hybrid battery for replacement.
Does anybody know if 2007 Mercury Mariner Hybrid has exactly the same battery as 2007 Ford Escape Hybrid?


BCM parameters during Start and Stall conditions

 

NiMH chemistry gets particularly sluggish as you approach 10°C.

Did you try re-balance?

MMH battery and FEH battery are the same for same year.

Recommend 08 or older to retain jump start.

 

Thank you.
I did re-balanced it once on Saturday. Two days after that there were no issues with starting. But nights were not as cold as today.
Will repeat it in couple of days. Maybe it'll get better.

 

Wanted to give the community some updates.
Issue came back in a week after multiple R-Balance so I decided to remove the battery and fully charge it based on instruction on this forum.
Fully charged the battery and fully discharged it 3 times during long weekend in an effort to revive dormant cells. Took four days to complete 3 cycles. It was completed on January 25.
At first - everything was OK. Voltage difference between cells came down to 0.13V - 0.19V. Driving range on the battery increased. But over the time voltage difference increased and came to even bigger 0.63V during discharge, up to 2.2V during engine start (similar to pre-full charge levels) and 0.25V-0.33V during charging.

Although I did not have start and stall issue since recharge - MPG is not that great - 27MPG (used to be 31MPG before all this happened).
Not sure how long it will run but looks like battery (or few battery sticks inside) is close to end of life. Also P0A1F-20 keep coming back (although not MIL). Forscan reports that Code is not present at time of request. I guess, this code is set once high Del_Mod_V is detected.