aspenpup

My 2008 Suburban (91k miles) battery went dead and I had to get jumped. I took car to local repair place (Pep Boys) and asked for a new battery since this battery is almost 5 years old. Instead of replacing, they tested battery and alternator and said both are good. They suggested I must have left something on to cause the drain.

I watched my dash voltage meter the next few days and noticed gauge goes about 15 volts for a few minutes, drops down to about the 14v level but then will drop down to 12.? volt range. I rarely look at gauge so I don't know what it is supposed to do.

Since voltage went so low, I assume my alternator was bad so I purchased a new one. Just to play it safe, I installed a yellow top battery (about 2 years old).

I was disappointed to find that I was still getting similar voltage readings. Just to eliminate the possibility of a bad dash gauge, I hooked up a digital multimeter to the battery and watched both (long leads from battery to meter in the cab). The multimeter matched the dash gauge.

So, what is 'normal'? What do I do, if anything? It make sense that voltage will go high to charge the battery. It also makes sense to drop as the battery is charged. The part that worries me is the voltage dropping down to 12.9v.

Basically, here are the average of my readings (I recorded 10 road trips)
Starting battery voltage before start: 12.5v
Immediately after start: 15.00v
About 5-10 mins after running: 13.9v
About 10-20 mins after running, but not always, drop to: 12.9v

By the way, I put the yellow top on a battery charger just to make sure it was fully charged.

So, any comments? Does this sound right? If not, what can I check next? I was thinking of buying a 'regular' battery to replace the yellow top just in case this deep cell battery was causing a problem with the readings.

Quite frankly, I was expecting the voltage to hoover around the 14volt range and stay there. I am planning a 500 mile trip next week and I don't want to find out the hard way that the battery is not charging and I find myself dead on the highway.

73shark

Sounds like your electrical system is performing normally both before and after you threw several hundred dollars at it after being told that. Not sure what the circumstances were before the battery was too low to start the truck. Is that the only time it happened? Had the radio or other electrical items been used w/ the engine off before? Has it happened again w/ the new parts?

BTW, the readings you are getting are normal. With the NBS GMT900 trucks, the computer controls the alternator output and you might even see <12V readings on trips. I've seen mine range between about 11.5-14+V.

You'll need to measure the current draw w/ everything off and then start removing fuses 'til you find the circuit that's drawing the current. Not sure what the normal quiescent current draw should be but would expect it to be less than tens on milliamps.

cleveland63b

looks good to me, at most I would of replaced the battery due to age

kevinkpk

N O R M A L!
The battery will only take so much, the rest is used for the electrical load, in simple laymens terms.

aspenpup

Thank you for the replies, I feel better now. The 'old' battery went dead twice on me so that is why I gave up on it, especially since it was over 4 years old. I do feel bad about buying the alternator, I wish I had not turned in the core.

"Just in case", I am going to bring a jumping battery with me on trip next week since it will be freezing (going from SoCal to Lake Tahoe). I don't want to get stuck.

73shark

You can store it in the spare battery tray on the driver's side up front. Might take a battery maintainer w/ you to charge it up before you return. Harbor Freight usually has them on sale for $5.

in2pro

I keep my deep cycle battery in the front tray... here is how I did, see post #40
https://chevroletforum.com/forum/tah...ay-3963/page4/

Magrogers

We had the same issue with our 2008 Suburban I replaced the Mega 175A fuse which is located behind the battery. Very easy fix with a cheap fuse. We haven't had any problems since I replaced this fuse. FYI the dealership kept telling us it was a bad battery, we took that "bad" battery and put it in our other car and it started up right away. I started researching online and discovered the mega fuse, for a part that cost less than $5 I thought it wouldn't hurt to try it. I'm kind of mad that the professionals at the Chevy dealership couldn't figure this out.

SWHouston

Since you've eliminated the obvious, you might have a amp test done on the starter.

{tpc}

Another here that thinks your charging system is acting normal. These things has a pretty intelligent system, and due to the overall health and charge of the battery, can very the amount of voltage going to it at any particular time. I think there is like 4 steps or something. I looked it up once, because I too freaked out the first time I saw it happening.

Personally I think you have a bad battery. I recently replaced mine, with a yellowtop optima, because it was bad. It had about 1-2 days on it tops, and then it was a crapshoot if it had enough charge in it to get to kick over. But if you drove it regularly, you wouldn't have noticed it, and even the gauge would have fooled you. I knew what it was due to having to perform some work on the truck and just leaving things like the interior lights on for a few minutes or other minor things and it would require a jump. Once I was charging the battery, it wasn't at the full charge point but I could hear it making bubbling or some other strange sound.

That battery was old, came with the truck when I bought it used, and everything pointed to it being a problem. Cold out? Harder to start. Warm? No problem....just general stuff like that.

I am surprised they didn't find the battery was bad, but I doubt those things are 100% foolproof.

I do wonder what part the mega fuse might play into it, but as I see it, isn't it just a fuse and nothing more, nothing less?