I have a 600Ah bank, made up of Lifeline AGM batteries. Using all electric appliances, my overnight consumption is typically 125Ah. (I have seen as high as 200Ah.)
In my case, 5C is moot, as with 2x125A alternators, the best I could ever achieve is about C/3. (Now the RAM is equipped with 2x200A alternators.) The best that my solar kit can provide is 30A, which is much lower, but still very useful as the solar kit keeps charging long after the engine stops.
The 2013 Chevrolet Silverado has a very sophisticated charging system. When I took delivery of my camper in December it was cold and the truck had been sitting for several months during contraction. My usual charge voltage was 15.5v. My guess is that between winter cold and batteries that had been sitting for a while, the Chevrolet went into some combination of temp adjust and equalization. Once that was complete, about a month later, the voltage dropped to about 14.5v and has stayed down. Will have to see what happens next winter.
This is an extract from the GM shop manual. It specifically notes that the Chevrolet uses a shunt and is temperature compensated. This is a far cry from the voltage regulators of some years ago.
=============================================================================================================================
CHARGING SYSTEM OPERATION
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Battery Sulfation Mode
• Charge Mode
• Fuel Economy Mode
• Headlamp Mode
• Start Up Mode
• Voltage Reduction Mode
The engine control module (ECM) controls the generator through the generator turn on signal. It monitors the generator performance though
the generator field duty cycle signal circuit. The signal is a 5 volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100
percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The following table
shows the commanded duty cycle and output voltage of the generator:
The generator provides a feedback signal of the generator voltage
output through the generator field duty cycle signal circuit to the
ECM. This information is sent to the body control module (BCM).
The signal is a 5 volt PWM signal of 128 Hz with a duty cycle
of 0-100 percent. Normal duty cycle is between 5-99 percent.
Between 0-5 percent and 100 percent are for diagnostic purposes.
Commanded Duty Cycle Generator Output Voltage
10% 11 V
20% 11.56 V
30% 12.12 V
40% 12.68 V
50% 13.25 V
60% 13.81 V
70% 14.37 V
80% 14.94 V
90% 15.5 V
===========================================================================================================================
The obvious point is that the Chevrolet runs well above 14v for a lot of the time. I have no reason to suspect that Ford and RAM are any less sophisticated.
With the batteries in parallel, I can typically recoup 200Ah within three hours of driving.
YMMV, but the simple fact remains, with proper wiring, the original poster's Chevrolet is capable of much better performance than he is seeing.
I find that the biggest reason that people doubt this is that they have simply never seen a truck with wiring much larger than 6 AWG and so they accept that as the limit of the system.
