The indignities...

wsteele said:

Here is the link for the tender I bought.

https://www.amazon.com/CTEK-40-206-5-0-12-Battery-Charger/dp/B00CD44RQO/ref=sr_1_1_sspa?crid=1HKIS0KB235Y4&dchild=1&keywords=ctek+40-206&qid=1614102071&sprefix=ctek+40,aps,217&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyMFMxSlI1UzJZUkxaJmVuY3J5cHRlZElkPUExMDQxOTE2MVJIRzJQQTU0SkExMCZlbmNyeXB0ZWRBZElkPUEwNTI1Njk0Mk5EQjUwVklGRVZLVSZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

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Rocket Man said:

Thanks. I’ll probably get that one if I buy an AGM battery for the Silverado. It’s just running a lead acid one now and it and the optimate has been working fine. But I’m sure it’s only a matter of time before it needs a new battery with the way that truck is driven and the fact it always has a high current draw with it running 2 Viair 485 compressors.

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iamdub said:

As a test, you could unplug the RVC sensor and see if the voltage goes up and stays up. It's on the negative battery cable, not far from the battery post.

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wsteele said:

I decided before disconnecting the RCV sensor, I would check the charging voltage with a meter, versus just relying on the gauge in the cab (which has always shown good voltage). At idle, I was getting 14.5 -.7 volts to the battery, so I think I don't have a problem with the RCV system limiting charging voltage. I then decided to drain the battery for a half minute or so (lights, seat heaters, fans, etc.), then start it, running all my normal accessories, let it idle for 10 minutes, shut it down and check the voltage at the battery immediately. The voltage at the battery was 12.7v, which is .4-.5 volts above where I have read it each time after a few hours.

I think my problem is a battery that has seen it best days. It might be because I had neglected it for too long before I swapped alternators or might be just a crappy Napa AGM battery. I did see a TSB GM published for 2007 Model year Yukons (and all others of this ilk), where the BCM needs a refresh to update the power saving algo's. I don't know if my BCM is affected and if it is, whether it might have had the new rev sw flashed, so I will ask my service rep to check. Maybe I will get a chance to use my new Tech 2 to update my BCM, if it ever gets here from China.

Also, maybe when I get that fancy tender, the conditioning sw it has might help restore the battery to some degree. Hope so.

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iamdub said:

I should clarify: I didn't mean that you may have a problem with the RVC. I just meant to remove it from the equation to see if your battery and alt were actually fine and your lower voltages were just because it was cycling as normal. That's what it does- it reduces or stops the output from the alternator to not needlessly overcharge the battery. I don't think it's active at idle, so your volts would be the normal and expected 14.5ish. If your alternator is charging strongly and your battery is taking that charge quickly, as in during your short trip to the grocery store, the RVC would reduce or stop the charge from the alternator and let your vehicle run or run more off of the battery, and this may have been when you noticed the lower voltage- during one of those "charging off" cycles.

I still agree to the tender. With a low-amp model, you should leave it on the tender as much as possible. According to what I read, I should leave mine on for at least two weeks to really take effect. But, mine is a 1.x amp model. Yours is about four times the power, so it should do whatever it's gonna do much quicker.

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wsteele said:

I am not well enough acquainted with how the RVC works to know if what I am watching on the dash gauge is a fair representation of what the battery is getting. Frankly the dash gauge slowly moves up to the mid 14v range right after startup and doesn’t move much from idle warm up, around town and back. I watched the gauge like a hawk in my afternoon around town today and the voltage was always over 14, rough guess at least 14.2v. If what the battery is seeing is a different voltage than I see on the gauge because the RVC is throttling the voltage to the battery, then I think your supposition that the RVC might be interfering with a quick recharge may in fact what is happening. On the other hand, if what I am seeing on the dash gauge is the voltage the battery is seeing, the RVC isn’t throttling the voltage.

Looking at what seems to be happening on the surface is the battery takes something above 80% pretty easily, but it doesn’t stay up there. It seems to discharge down to something closer to 50% (12.2-12.3v) very quickly. A chunk of that “discharge” will happen even if the battery is disconnected.

So it may be that the current battery condition is related to an RVC throttling voltage, a down rev BCM or maybe the more likely culprit a failing alternator left in too long which took its toll on the battery.

I am going to hold off buying a new battery until I get to see what possible effect the new tender might have on the clearly subpar battery condition. In the interim, I plan to see if my BCM sw has the update called out in the TSB.

Does that make sense? Or am I still missing some part of the picture?

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iamdub said:

Nah, we're on the same page now. I was hoping it was just the RVC doin it's thing and your battery actually wasn't bad. But, now you at least know of one other possible factor.

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wsteele said:

So my CTEK charger/tender came today. It has a conditioning mode, theoretically reversing some of the degradation a battery might have suffered over time. It will be interesting to see if the reconditioning processes reverse any of the apparent degradation the battery clearly has suffered.

I got it hooked up and it seems to be functioning. It is a whole lot quieter than the Diehard battery charger I was using to keep recharging the battery between uses.

Right now I am mulling what hard wired location I want for the pigtail that will be connected to the battery for ongoing tender duty. I have mixed feelings about having a convenient and unobtrusive place for the pigtail (say coming through the grill) as I can see myself in a preoccupied moment just backing the truck out and dragging the whole kit and caboodle down the street before I realize I forgot to disconnect the tender. That is one positive of having to open the hood each time to hook things up. I won't forget to unhook things with the hood up. Decisions, decisions...

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