Lesson learned: bring a voltage tester to the store

DemoFly

DemoFly

Joined
Jun 3, 2012
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Location
Bremerton, WA
I’ve been diagnosing a parasitic drain and reverse engineering my new dash camera I installed. Wondering why my new AGM battery drains to 12.2 overnight.

Would have saved me a couple hours of testing and several days of overnight draining if I just ensured the battery was good when I bought it.

Yes, folks. Walmart platinum AGM sticker 12/24 has a resting voltage of 12.2.
 
I found that AGMs sit on the shelf a while because they are significantly more expensive...so that would automatically be questionable.
But if what you're saying is true and it has a 12/24 sticker then that's surprising.
Your point is spot on, don't buy a battery without testing voltage.
 
on my summer fun car a 2001 TT roadster i use a "quick disconnect" to stop battery drain, cheep + eze!!
 
it's a good lesson to learn.. I used to take a multi-meter with me. Now I take my battery tester with me, sure it's a resistance not carbon pile tester but it's more than capable of showing the voltage and if a battery is bad when brand new. I just recently tested some group 35's at walmart (maxx model) for my relatives vehicle and some were better than others, voltage and resistance numbers. it's an imperfect world, you try to get the best you can out of the batch.

Try charging up the battery and see if it holds a better charge level at rest.
 
I just landed in Detroit at 2:00 to a stone dead battery in my wife’s 6 month old Altima. Yes the car drew voltage for 10 days but the battery tested at 60% when AAA showed up.
 
D1dad said:
I just landed in Detroit at 2:00 to a stone dead battery in my wife’s 6 month old Altima. Yes the car drew voltage for 10 days but the battery tested at 60% when AAA showed up.
Click to expand...
Let's say conservatively that the battery should have an A-h capacity of 60. (Likely more.)

Let's also say that the dark current should be no more than 30 mA.

30 mA x 24 hrs = 720 mA-h/day.

Over 10 days, that should be only 7.2 A-h gone.

Sounds like either a weak battery or excessive dark current.
 
Number_35 said:
Let's say conservatively that the battery should have an A-h capacity of 60. (Likely more.)

Let's also say that the dark current should be no more than 30 mA.

30 mA x 24 hrs = 720 mA-h/day.

Over 10 days, that should be only 7.2 A-h gone.

Sounds like either a weak battery or excessive dark current.
Click to expand...

I don’t know what all your numbers mean lol. I do know the car was titled in May and from my house to Detroit metro is an hour and a half, so it wasn’t short tripped. When triple A got there with their jump box, that battery had 0% charge and tested at 63% health. Our 18 rogue sat in the same garage for 5 weeks and my 21 Altima has set there 10 days many a time. I dropped it at the dealer last night and picked up a loaner. Apparently the testing for a warranty battery takes a few hrs. I’d have just paid AAA for a new battery or stopped at Walmart on the way home had I not been so upset. This was after my 6am flight was delayed till noon. I’ve got an ancel tester and went through all my cars and my rogue with an almost 4 yr battery was tested g at 87% while the new Nissan was testing at 95% a month ago. Maybe there’s some parasitic draw somewhere? Don’t know.
 
12.2 V is terrible. My AGM was shipped from Advanced Auto to home and read 12.73V. It was manufactured in July 22 and recharged in Dec 22. The BA101 reading and purchase was in Dec 2023.

From the Odyssey documentation, a fully charged AGM should hold a charge 6 to 12 months and is storage temperature dependent.



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IMG_7188.webp
 
Last edited:
researcher said:
it's a good lesson to learn.. I used to take a multi-meter with me. Now I take my battery tester with me, sure it's a resistance not carbon pile tester but it's more than capable of showing the voltage and if a battery is bad when brand new. I just recently tested some group 35's at walmart (maxx model) for my relatives vehicle and some were better than others, voltage and resistance numbers. it's an imperfect world, you try to get the best you can out of the batch.

Try charging up the battery and see if it holds a better charge level at rest.
Click to expand...
I am guessing your battery tester is a conductance battery tester and not a resistance.
 
If I owned a battery store I think I would be happy to test any battery for someone but not sure I would want people doing their own testing. Imagine if you connected up a carbon pile tested that had been dialed up to 400 amps. Giant spark. (Normally you connect the carbon pile tester when it's dialed to zero. Then dial it up to 1/2 CCA and wait for the beep, read the voltage and dial it back to zero, then disconnect).

People should be wearing safety glasses if they are doing anything more than looking or carrying the battery.
 
So continuing to educate myself in reading this and anticipating I will need to replace two or potentially three batteries: an H8/49 AGM in our 3 series BMW, and a starter and/or house MARINE battery, regular wet cell type, on our sailboat. I have purchased the HF tester: https://www.harborfreight.com/12v-digital-battery-and-system-tester-58759.html

What numbers should I be looking for at the store shelf for voltage, etc. Plan to source from Costco, Walmart and also considering the local auto chain outlets and Batteries Plus. As I understand it my older sailboat charging system is not compatible with AGM marine batteries so have to stay with marine wet cell.
 
RaymondP said:
So continuing to educate myself in reading this and anticipating I will need to replace two or potentially three batteries: an H8/49 AGM in our 3 series BMW, and a starter and/or house MARINE battery, regular wet cell type, on our sailboat. I have purchased the HF tester: https://www.harborfreight.com/12v-digital-battery-and-system-tester-58759.html

What numbers should I be looking for at the store shelf for voltage, etc. Plan to source from Costco, Walmart and also considering the local auto chain outlets and Batteries Plus. As I understand it my older sailboat charging system is not compatible with AGM marine batteries so have to stay with marine wet cell.
Click to expand...
I would double check the charging system on sailboat. Some marine charges can be set (via various methods) to charge different types of batteries. Also many marine chargers that can charge a flooded cell can also charge a plain AGM on the same setting. But not a Odyssey or Optima AGM. That take a different setting.

If you can get an AGM on your sail boat that is what I would suggest.
 
Donald said:
I would double check the charging system on sailboat. Some marine charges can be set (via various methods) to charge different types of batteries. Also many marine chargers that can charge a flooded cell can also charge a plain AGM on the same setting. But not a Odyssey or Optima AGM. That take a different setting.

If you can get an AGM on your sail boat that is what I would suggest.
Click to expand...
My sailboat charger states only for wet cell batteries, as it is an older boat. Possibly AGM batteries were less common at the time (1986). Is there a minimum charge rate (amps/volts) that would be required to charge an AGM battery. Size is 24.

A retailer that sells marine batteries stated as long as it charges at over 13 volts it will be fine for AGM batteries. Is this true/correct?
 
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