Charging 12V Battery Using Under-hood Contacts

[dfh]

I have had a 2013 SEL, Equipment Group 303A, for about 1 yr.  Two years ago an independent shop replaced the 12V battery with a OEM Motorcraft.  Among the service records I received from the previous owners, there is no indication of an earlier battery replacement.

 

About 6 months ago, one morning I found the CMAX wouldn't start and determined the 12V battery required charging.  I charged it for an hour or two using a Sears 12V car battery charger (purchase in the 1960s) using the under-hood contacts.  At the time I suspected that the auto-headlight-turn-off feature had failed, and I stopped relying on that feature.  Now I wonder if the problem was of the sort addressed by Ford's Customer Satisfaction Program 15B04, which has been discussed on this forum (along with lots of dead 12V battery issues).  However, according to Ford's records, CSP 15B04 module reprogramming and wire inspection was done by a Ford dealer on 7/13/15.

 

Recently I again found the battery voltage was too low to allow the CMAX to start.  When I tried to charge it with the Sears charger using the under-hood contacts, as before, the charger's current meter pegged at 7A.  I quickly unplugged the charger.  Since the charger is only rated for 5A continuous, I limited the current using a high-wattage, 1- or 2-ohm resistor.  However, something on the right-hand side of the under-hood equipment then began to click is a repetitive sequence, and the current drawn from the charger changed several Amps in synchrony with the clicking.  I found that when I limited the current to around 3A by using 3 ohms, this clicking stopped and the current was constant.

 

Although it was left charging at around 3A for more than 24 hours, the battery voltage did not increase to the point the CMAX would start. 

 

I was able to recharge the battery by disconnecting the connector from the battery positive post and using the Sears battery charger connected directly to the isolated battery.

 

A Ford dealership service department reports that the battery has passed their elaborate battery stress test, and they didn't find any reason why the battery voltage was so low in the first place.

 

Does anyone have any idea what could have been causing the clicking I heard when the charging current was greater than 3A while I was using the under-hood contacts that are there to permit battery charging with access to the battery?

 

Does anyone have any idea what why I couldn't recharge the battery using hundreds of watt-hours of energy, yet the battery passed the dealership's stress test?  It seems the energy must have been dissipated somewhere other than in the battery, but where?

 

Thanks for any ideas,

 

David

[SnowStorm]

I've had a number of dead 12V events in the past and once it did what you describe.  Once "dead", the voltage can be very low, like 4 volts in my experience, and I can see a charger easily going into an overload condition if it doesn't have adequate current limiting.  In my case. outside lights on the car were flashing and, IIRC, there was also a clicking sound.  My charger is electronic and can be set to 2, 10 or 15 amps.  I don't remember if I changed settings or what but things eventually settled down and the battery got charged.  I suspect your theory is correct.  Something is always drawing enough current (3 amps) to prevent charging.  If the voltage goes up enough, other things turn on, more current is drawn from the charger, voltage drops and you get the oscillation.  The sneaky thing about all this is that the battery can go way past "100% discharged" (below 10.5 volts) and the car may still "start" since it only needs to turn on some electronics and close the contacter to the HVB.  I think the cutoff point is at least as low as 8 volts.  Below that value the car won't start but the battery was "dead" long before.   Keep a jump starter with you and use that to start the car from under the hood (they can put out a lot of current).  Eventually, these repeated deep discharge events will weaken the battery to the point it won't pass the stress test, but until then, it will test OK.