It was -31C overnight here a couple of days ago and I didn't plug my truck in. In the morning I got a very slow cranking speed and no start. I plugged it in and took my car to work. When I returned, it started easily and I moved it into the garage and put a trickle charger on the pass side battery (2A, then up to 10A charge), then repeated the same for the driver's side battery. After 4 or 5 hours, I disconnected the charger and moved the truck back outside and plugged it back in. THe battery charger showed "full charge" for both batteries.

Yesterday morning I started it and noticed that the alternator is putting out 16A+ when the truck is cold. It makes no difference while driving for a while, but after I park the truck and come back to it and start the engine, the guage shows 13-13A. If I leave it overnight, it charges in the 16A+ range again after I start the engine. I'm suspicious about the condition of one or both of the batteries - possibly not taking a charge properly. In fact, I was surprised the engine wouldn't turn over quickly enough to start after one night of -31C. Last year it started in -35C weather. I apreciate it is better to plug in on very cold nights, but when one makes a mistake ...

thanks for your comments,


kayjh

 

I would get the battery's load checked. Just be sure that they are checked independent of each other. In other words, remove both ground cables. I'll bet that one has gone sour.

 

-31 was that C or F? Are you running synthetic oil?

At low temperature our lead acid battery efficency goes down, the grid heater also gives the batterys a pretty good hit while the wait to start light is on. At those temps unless you run a good syn oil you are going to need massive cranking amps. I think that it would be wise to use the syn oil and plug in at night.

Does your truck have an ammeter or a voltmeter?

Below is some info from a RE energy site on battery performance vs temp. I think it explains your 16V reading.

"Battery charging voltage also changes with temperature. It will vary from about 2.74 volts per cell (16.4 volts) at -40 C to 2.3 volts per cell (13.8 volts) at 50 C."

"Battery capacity (how many amp-hours it can hold) is reduced as temperature goes down, and increased as temperature goes up. This is why your car battery dies on a cold winter morning, even though it worked fine the previous afternoon. If your batteries spend part of the year shivering in the cold, the reduced capacity has to be taken into account when sizing the system batteries. The standard rating for batteries is at room temperature - 25 degrees C (about 77 F). At approximately -22 degrees F (-27 C), battery AH capacity drops to 50%. At freezing, capacity is reduced by 20%. Capacity is increased at higher temperatures - at 122 degrees F, battery capacity would be about 12% higher."





Regards,

Jim B

 

Windyr,

It was -31C (-24F). The truck has a voltmeter (I believe). From your post, it looks like it may be normal for output to be as high as 16 volts under the right circumstances. Given that the truck started in -35C last winter, I'm betting one of the btteries is not performing properly. I'm going to take it in to the dealer on Tuesday for an AVR test.

kayjh

 

I suspect that you are correct about the battery not being as hat as when it was new. Those temperatures really demand top performance.

Regards,

Jim B

 

Unless you disconnected the battery cables, you charge both batteries at the same time when you connect a battery charger to either battery. The positive leads on both batteries are connected to each other.

Your voltage readings are normal.

If you replace one battery it's a good idea to replace both at the same time.