Charging advice required

[s2kbobby]

I bought my 2013 BRZ new in June 2012.

In December 2015 it failed to start several times. Twice I boosted it and several miles later it again failed to start. A check of the charging system showed 13.8 volts at the battery with the engine running.
I replaced the 3 year old battery, believing that was the cause.

Today, less than a year later it failed to start again. (Temps close to 60F) The last time I started it was 4 days ago and it SEEMED to crank somewhat slowly but started immediately. I should have taken that as a sign of trouble.

No lights or accessories were left on to my knowledge. I have no mods, electrical or otherwise.

My question is:
Is it possible for a charging system to be only partially able to charge the car yet supply 13.8 volts? That could explain why the car will run on a boost yet the battery won't charge enough to start it after a few miles of daytime highway driving.

Every car I have owned would start following a battery boost and then a drive of several miles. This is common in cold weather Canada. This battery didn't last year.

It could be a bad battery (Subaru supplied) or I could have a partial charging issue.

Thanks in advance

[jvincent]

13.8V should be sufficient.

Are the battery cables in good shape and properly connected?

[humfrz]

It's my understanding, that although the alternator is putting out 13.8 volts, if the battery has been discharged totally, the alternator will not bring it back up to full speed.

The alternator usually will just replace the electrons consumed under normal operation.

I would suggest you put the battery on a slow charger to fully charge it.

If that doesn't do it, have it "load tested" at an auto shop.

If it fails the load test ..... time to buy a new one.


humfrz

[s2kbobby]

Originally Posted by humfrz

If that doesn't do it, have it "load tested" at an auto shop.

If it fails the load test ..... time to buy a new one.
humfrz

A year old battery? I find it hard to believe, however my past experience is driving Honda's. Perhaps I should lower my expectations.

[FRS Justin]

Voltage is not amperage.... You can have 13.8 volts and 10 amps and your not going to start the car... Have someone crank the car and you watch a volt meter at the battery, if it drops to single digits like I assume it will get a battery...

[jvincent]

The other thing to remember is that the output current of the alternator will vary with RPM. Higher RPM = more current and higher voltage too.

So, if you get a jump and just idle for a few minutes that's probably not enough. If you go for a 20-30 min drive it should be plenty.

[guybo]

Voltage tells you state of charge, it tells you nothing about the state of health of the battery UNLESS you have a bad cell in which case voltage tells you a lot. You can have a battery that is fully charged at 12.6V but it is junk because the cold cranking amperage sucks. A battery may take a surface charge, but can't take a deep charge. It happens.

A regular flooded lead-acid battery has 6 cells. They have lead paste on steel plates and immersed in an electrolyte of sulfuric acid and demineralized water with other chemicals. All batteries are not the same, they vary in amount of lead, the amount of electrolyte and the chemicals in it. Each cell produces 2.1 volts. 6 x 2.1 = 12.6 which is a fully charged battery. The cold cranking amperage varies by every type of battery, voltage does not. Voltage is always 12.6V fully charged and new, CCA depends on make and group size. CCA depends on the state of each cell and depends on the amount of lead paste, how deteriorated the lead paste is (in every charge cycle, the lead paste loses some electrons and the negatively charged paste [there's negative and positive plates] turns black), the state of the electrolyte and how much sulfation has occurred. Sulfation is caused when the battery gets drained usually, or when a battery sits.

If the battery is at ~12.6V and fully charged but drops to under 9V when you crank it, the battery is probably junk. At the same time, you can have a good battery at 10V (it'd be discharged) that starts the car if the CCA is good enough. I've also seen batteries with 10.5V with a bad cell that cranked the car over because it had 1 bad cell but 5 good cells.

TL;DR Get it load tested, voltage tells you jack squat.

As for the alternator, the voltmeter gives you an idea of what's going on, but if it has an open diode or some other electrical issue like that, the voltmeter won't pick it up and you'll fry one battery after the other. That needs to be properly tested also.

If you are a AAA/CAA member and you are in a territory with full battery service, burn a call (you get 4) and have your battery and alternator tested. The battery test is not very good. The alternator part of the test is pretty good if the battery doesn't have an electrical issue that messes up the test somehow.

[humfrz]

Originally Posted by jvincent

The other thing to remember is that the output current of the alternator will vary with RPM. Higher RPM = more current and higher voltage too.

So, if you get a jump and just idle for a few minutes that's probably not enough. If you go for a 20-30 min drive it should be plenty.

A couple of reads for your consideration .....

http://carbibles.blogspot.com/2013/0...arge-your.html


https://www.optimabatteries.com/en-u...dead-batteries


humfrz

[s2kbobby]

Well, a charging system test indicates the battery and alternator are performing to specification. The battery measures at 740 cold cranking amps and delivers 11.92V at startup. The alternator charges at 14.38V.

It's all well and good but still a mystery why I sometimes find a dead battery in the morning.

I hate intermittent problems.

[steve99]

Originally Posted by s2kbobby

Well, a charging system test indicates the battery and alternator are performing to specification. The battery measures at 740 cold cranking amps and delivers 11.92V at startup. The alternator charges at 14.38V.

It's all well and good but still a mystery why I sometimes find a dead battery in the morning.

I hate intermittent problems.

Do you have any non standard accessories, ie media system, dash cams , alarms etc.


devices plugged into obd port ?


You might need to monitor the standby current draw when ignition is off.


Any time you deeply discharge a car battery (they don't like this treatment and it shortens their life) its a good idea to put a battery charger on it overnight at least to get it back to peak condition. even if it started car ok.

[renfield90]

Originally Posted by s2kbobby

It could be a bad battery (Subaru supplied)

I found the problem.

OEM batteries are notoriously poor quality. I got 2.5 years out of mine which was pretty good considering my climate.

Recommend you get the next battery from your local parts store, and hook it up overnight to an external charger 2x per year. I have made a cheapo parts store battery last 6+ years that way.

[phrosty]

No headlights/AC, mine goes 14.1 (cold start) -> 13.2-13.8 (battery charged, seems to vary with temperature). With headlights/AC, from 14.5 -> 14.1.

My OE battery started having issues holding a charge after I forgot to unplug my Tactrix overnight one too many times. They really don't like to be deep discharged. I replaced it with an Optima yellowtop and everything is back to being good.

[humfrz]

Originally Posted by s2kbobby

Well, a charging system test indicates the battery and alternator are performing to specification. The battery measures at 740 cold cranking amps and delivers 11.92V at startup. The alternator charges at 14.38V.

It's all well and good but still a mystery why I sometimes find a dead battery in the morning.

I hate intermittent problems.

As mentioned before, have you cleaned the battery posts/cable connectors..??

They may "look" clean, but still have a layer of varnish that could prevent a good contact.


humfrz

[Ultramaroon]

Originally Posted by humfrz

A couple of reads for your consideration .....

http://carbibles.blogspot.com/2013/0...arge-your.html


https://www.optimabatteries.com/en-u...dead-batteries


humfrz

I blame this on manufacturers cheaping out on key components. I got sick of replacing the alternator on my Eclipse every time I left the headlights on. On my third one, I replaced the puny little internal regulator with a beefy F-150 external one. Never learned to shut off my lights but that alternator kept right on charging.