Aryay

I haven't used my car for at least a week and seems the battery died.
I was able to get a boost but after leaving it running for at least 30 minutes it didn't start again so I'm assuming I need a new battery.

I was just wondering what the recommendation is for a replacement battery and cost should expect about?

Thanks

Oro

If the battery is not that old, verify in fact it is the battery and not alt. Check the voltage across ther terminals at idle, running. It is possible the alt puts out enought to run the car but not charge the battery. A lot of batteries are replaced, only to find out shortly it was the alternator (or both).

Here was a recent talk on batteries on the same subject:

https://www.clublexus.com/forums/gx-...ery-again.html

Tootsall

Just put a battery charger on it overnight. It should be fine. If you make a lot of very short trips it may have slowly drained out, not getting enough reserve power from the alternator to get it back up before the next need to restart the engine. Or you may have a faulty circuit somewhere that is giving a parasitic drain to the battery overnight.

Aryay

thanks
It's about 8-9 years old but never had issues before.

When idling voltage is about 12v. When car is off after running it for about half an hour it decrease to 9.3-9.6.

Oro

8 to 9 years old is indeed up there.

But the alternator needs to put out at least 13.6V at idle to even keep the battery level (there is resistance to figure, and a “nominal” 12v battery is actually 13.1 or so (6 cells at 2.2v each), much less charge. Revved it should make more. A “new” alternator would typically put out 14.2 or more at idle and a steady 14.6v at any thing more. With the engine on, the voltage across the battery terminals is what the alternator is supplying (if any).

So it sounds like minimum, your alt is bad. Battery may still be good, though aged.

Aryay

Thanks

I picked up a new battery from Costco so you wouldn't recommend replacing it yet?

The thing is right now with the car off it reads at 10v (see picture)

and can't start it. Drove earlier for about 15 minutes and idled for about 20 minutes.

Also I believe the battery was at about 11v after turning off the car and now reduced to 10v. Shouldn't this mean the battery?

Oro

The battery won’t do anything until charged. That means putting like 75 amp/hours into it. That’s like 40 hours with a 2.1amp trickle charger, 8 hours with a 10 amp charger, etc.

It sounds like in fact it’s quite healthy. It’s not getting charged, but it recovers and then runs the car a while. That’s the sign of a healthy batter.

Then it seems you need a new alternator.

The new battery may or may not be needed. IME, Costco batteries have been the low-end Interstates and not very good. I got one at Firestone a while back (same as what Costco sells), it lasted 1.8 years. Firestone said they were so bad, they had to just quit selling them. They upgraded me to a better interstate (green top/MTP) and all is good. That battery has been in 7.75 years and is still very, very strong (I use a maintainer on it when not driven and desulfate periodically). Costco still sells that junk model last time I checked. There may be a different model at Costco now, but that’s what they were last time I saw. What’s the label on the battery you bought?

A denso reman alternator is really your best bet if you are not able to rebuild it. Do not go to O’Reilly at any cost or most auto-store brands. Terrible quality and high failure rate.

Aryay

was hoping this would solve the problem- I'm assuming should hold off replacing the battery, as might not be able to be returned then. I'm not familiar with Costco return policies.

So how can I tell for certain which it is? But the fact when the car was off it dropped from 11v to 10v- shouldn't that mean a bad battery? As once it gets a boost it runs fine until needed to start up again.

Oro

If the car is running and the voltage across the battery terminals is not 13.6 or more (and you REALLY want more than that), the alternator is NOT working. You have to correct that before anything else. Why your alternator is not working, I don’t know. Age, bad ground, etc. But you need to do two things:

1) Fix the alternator (verify the output voltage again if you are unsure)
2) Charge the battery completely (several hours at higher amperage, or DAYS at low amperage.)

Think of it like this: Your battery is a bucket of water. The water represents the charge/electrical energy. The alternator is like a faucet. It fills the battery when the car drains the bucket. If the faucet is not filling the bucket, and the bucket is empty. You are stuck. Have to fix the faucet, fill the bucket, and then see how things are working.

If this is unclear to you why, try googling about the subject until you get the basics of an alternator/battery system. Here’s a start:

https://www.airparkautopros.com/blog...er-in-your-car

That is in fact one of the cheap Interstate batteries that fail often. I would not put that in one of my cars, but lots of people do. If you have a Firestone nearby, see how much a green-topped Interstate is. There is usually an online coupon, and you can have the installation fee refunded if you install it yourself. That’s usually a solid battery deal. That is, if your battery is in fact bad or perhaps you just want a new one because of its age.

Aryay

Thanks

Mechanic thinks it's the battery as it started ok and voltage read as 13.7v once running.

He only has NAPA batteries, it's about 50 CCA less than the Interstate (650 CCA, 800 CA vs 700 CA, 875 CCA) and about $40 more with installation. Am I better off with the Interstate one or his and is this a DIY thing or better for him to install it.

jgscott

iTrader: (1)

The correct way is to go have the battery Load Tested on test equipment. Just taking reading of voltage at times tell nothing. It's the load pulled when cranking that counts along with a full charge. It can show 12 - 14 volts all day long. What matters is if the battery drop below a specific crank voltage with a load test.

Aryay

How can I get the battery to be a full charge?

Aryay

So when the car was on was getting 13.3v and battery was read at 100% by voltmeter. Now it's off and about half hour later reads at 12.1v and 66%. Would this mean anything to know if battery needs to be replaced yet?

Oro

See post #7 above. Apply amps with a charger until amp/hour total is about 75. These batteries have reserve capacity of around 100 to 120 amp/hours. 75 amp hours should top up a very low battery.

You have to get it fully charged, then load tested. Any auto parts store will load test it for you once it is fully charged. Can’t accurately test it without being fully charged. Or just use it and see if it re-charges from the alternator and working ok. Read the link above to help understand this system as it appears it is still unclear to you.

Any napa battery will be better than the cheapest Costco battery. I like interstate batteries overall, but the costco low-grade ones are junk, it pains me to say.

Aryay

Thanks. I don't have a charger at home so only way would be to drive it.

Thing is I don't usually go that far so it may end up using more power to start the engine than recharge the battery, but I'm wondering if checking the voltage while it's off every other day help to see if it drains quickly and is a bad battery?

Thanks for the link I do understand better what the alternator does.