After acquiring a 08 Mercury Mariner that had been sitting for a few months and wouldn’t start I hooked my scanner up and the only code I’m showing is P1A10 - Hybrid Powertrain Control Module - Battery Disabled. The HV battery is reading 234.12 v on my scanner. I’ve read about the small button on the driver side access panel on the side of the dash and after charging the 12v battery overnight and removing the key from the ignition I tried the little button to begin charging the HV battery but it just flash’s when I press it some other videos show the light on the button going solid and flashes once complete. I’ve tried a few times and even waited the 8 min then immediately checked the HV battery voltage and it had no effect. would anyone happen to know how to get this to work correctly. Any information would be greatly appreciated. Thank you.

 

What are you using for diagnostics?

HV jump starter places a very heavy load on the 12V. It is critical that the 12V be healthy and fully charged to insure optimal HV jump start operation. Given that the 12V has been sitting for 3 months, it's is a certainty that your 12V battery is NOT healthy, unless it was stored on a float charger or disconnected from the vehicle after fully charging. Cars pull a continuous load on their batteries... typically something around 15mA. That means most batteries left connected to non-running cars will drain their batteries completely flat within 1-3 months. Batteries drained completely flat and held at low voltage destroy themselves internally and sustain permanent damage. ANY battery subjected to this kind of abuse is a candidate for replacement - even if brand new.

Note also that even disconnected from a vehicle, wet cell batteries lose their charge pretty rapidly - typically about 30%/month. More expensive AGM batteries only lose about 3%/month. Any time a battery is below 80-90% state of charge, it begins destroying itself and sustainging permanent degredation.

300V is completely empty, so 234V is in bad shape. Discharged NiMH cells that have been sitting for a long time go into a dormant phase, where their resistance is several times higher than normal. When a charge current is applied, their voltage will spike artificially, cause the HV jump starter to fault and then rapidly fall. Additionally, in some cases, with cleared codes, turning the key on will engage the hybrid battery and the DC-DC converter to power any 12V loads. This will rapidly pull the HV battery voltage back down until the HV relay disengages. If you're not seeing the HV battery move at all, this is likely not the case.

A way around both issues is to attach a RUNNING jump vehicle to the 12V. The alternator of the jump vehicle will supply the jump start current while keeping the 12V battery voltage up. Try this first.

Recommend attempting jump starts every 10 minutes for an hour with a running 12V jump vehicle attached.

 

Thank you for that insight, I've wondered about it in the past but have never seen it described before. When the 12V battery on my 2010 FEH (which doesn't even have the button!) died last winter, I immediately disconnected it and did not attempt to key-cycle the vehicle *or* jump start it. There was also snow in the way, which would have complicated moving the FEH to connect the jumper cables.

What happened was that I walked out to the car on a very cold night to make a quick trip to the store. I hit the "unlock" button on the key fob, and the lights tried to blink, the doors *tried* to unlock, but the power locks didn't work and I was locked out of the car. I used the key, and once I opened the driver's door, I could hear various relays and so forth clicking in the dashboard. I instantly realized the 12V battery had conked out and I thought about what I should do, including putting the key in and attempt to start it. In the back of my mind I thought: "Wait a minute. This car has a DC-DC converter. If the 12V battery is really bad, the computer might command the DC-DC converter to pull current from the HV battery and drain it to a point that it will no longer start the ICE." At that point I would have been in really bad shape, because my car lacks the jump start button, and then my only options would have been to build a charger or tow the car and get the HV battery charged. And it was COLD outside. I wanted no part of that.

Instead I popped the hood, disconnected the 12V terminals, went the next morning, bought a new 12V battery and installed it. The car started right up, no problems. The 12V battery was the *original battery* that came with the car in 2010.

 

Good choice.

While it has a DC-DC converter, the 12V must be of sufficient health to power the various computers through their POST and handshaking phases.

Not at all uncommon for hybrid 12V to last substantially longer than typical 12V due to the fact that they rarely provide more than 20A and spend their lives at 95-100% SoC.