Battery level

devildog2621 · April 27, 2023

Threw charger on my battery today. Batteries less than a year old. The charger said The battery was at 40%. What would be the cause of a low battery? Don't believe it's a drain. GMC Sierra 1500 2013.

dsr611 · April 27, 2023

Dead cell, bad alternator, parasitic draw from somewhere, battery could have been bad to begin with

devildog2621 · April 27, 2023

What's the output of the alternator be? It's stock.

CamGTP · April 28, 2023

These trucks have a smart charging system, the computer will determine what voltage the alternator needs to charge at.

So it can be anywhere from 13 volts up to 15 volts depending on the demand of the computer.

swathdiver · April 28, 2023

21 hours ago, Matthew J M Devildog Thompson said:

Threw charger on my battery today. Batteries less than a year old. The charger said The battery was at 40%. What would be the cause of a low battery? Don't believe it's a drain. GMC Sierra 1500 2013.

If the truck is sitting for a few days and then you make some short runs the battery never gets a chance to become fully recharged. The computer system typically keeps the battery at a state of charge in the 70-80 percent range to maximize its life. A battery being jammed to 100% all the time does not last long.

GMs replacement spec is 64%, a battery that cannot maintain a state of charge at that number (12 hours after charging) is out of spec and ought to be replaced.

If she does sit for periods of time, put a tender on it. This will also de-sulfate the plates and allow the battery to take a "full" charge again. I got another year out of a battery by doing this once.

This generation of trucks were not designed to charge AGM batteries. They won't last as long as they could have. Just read a caveat in my shop manual, it says an AGM can be damaged if charged to more than 14.5 volts. Our system can charge at 15.5v if the computer decides to.

Edited April 28, 2023 by swathdiver

devildog2621 · April 28, 2023

Thank you for that information. I do have an AGM battery. I have a voltmeter on the dash and it never reads more than 14.4. I didn't realize they only maintain a 70 to 80% charge. And it will sit for 3 days and then I'll make a short trip less than 5 mi , then it'll sit a couple more days.

swathdiver · April 30, 2023

On 4/28/2023 at 8:18 AM, Matthew J M Devildog Thompson said:

Thank you for that information. I do have an AGM battery. I have a voltmeter on the dash and it never reads more than 14.4. I didn't realize they only maintain a 70 to 80% charge. And it will sit for 3 days and then I'll make a short trip less than 5 mi , then it'll sit a couple more days.

Take her out for a highway run once a week and or put her on a battery tender.

diyer2 · April 30, 2023

My 2cents. it sits 2-3 days with the power draw for the computers. Then a short trip with running lights, radio, heater on. Not enough time to charge the battery, battery tender is a must.

devildog2621 · April 30, 2023

Thank you. What is a battery tender?

txab · April 30, 2023

3 hours ago, Matthew J M Devildog Thompson said:

Thank you. What is a battery tender?

https://www.amazon.com/Battery-Tender-021-0128-Maintain-Damaging/dp/B00068XCQU/ref=sr_1_5?crid=1DE7HY41PPQ4O&keywords=battery+tender&qid=1682889730&sprefix=battery+tender%2Caps%2C335&sr=8-5&ufe=app_do%3Aamzn1.fos.006c50ae-5d4c-4777-9bc0-4513d670b6bc

devildog2621 · April 30, 2023

Thank you. What is a battery tender?

28 minutes ago, txab said:

https://www.amazon.com/Battery-Tender-021-0128-Maintain-Damaging/dp/B00068XCQU/ref=sr_1_5?crid=1DE7HY41PPQ4O&keywords=battery+tender&qid=1682889730&sprefix=battery+tender%2Caps%2C335&sr=8-5&ufe=app_do%3Aamzn1.fos.006c50ae-5d4c-4777-9bc0-4513d670b6bc

Thank you