New battery "charge up" time

[rationull]

As I mentioned in another post I just replaced the OEM battery in my car. Monitoring the voltage on my scangauge it hasn't impressed me all that much yet. What I mean is the voltage is a couple tenths lower than I'd expect it to be with the dome lights on, for example. Maybe I'm expecting too much but I thought maybe a new battery wouldn't show a drop with such low load. Also, normally the alternator will stop charging when not needed after the car's been running for a while and the electrical load is low. I can see this on my SG when the voltage drops to the low 12s while running. This is behavior as designed, and it's pretty predictable, but I haven't seen it with the new battery yet when I'd expect to.

Is it possible the battery was just discharged enough that it'll take quite a while driving to get it charged up? How long should it take? I didn't hook it up to a charger or anything, and it was manufactured in September so it did sit on the shelf for a few months.

 

[Jim 5]

I'm not sure how to answer your question, however, I do know that your alternator will blast a discharged battery with 30 amps or more. This will give it a "top charge" (IIRC) but not an ideal charge.

A better process with a brand new battery that's been sitting on the shelf is to trickle charge it slowly to bring it up to condition before installing (or after installed, which is just as good in your case). Then your alternator can top it off thereafter.

 

[UNC017]

Don't trust a scan gauge for tenths of a volt accuracy. Use a real voltmeter.

What you're seeing sounds normal to me, EXCEPT you should NEVER see the voltage drop "to the low 12s" at any time while the engine is running. That indicates a problem with the charging system... assuming that the voltage is really doing that and its not just inaccuracy of the PCM voltage measurement reflected by the scan gauge.

 

[oilboy123]

You are getting good advice.

 

[rationull]

I dug up my original post on the low voltage while running issue -- here's a link. I'm not saying it's a good design but I don't think it's a functional problem. Good point on the scangauge voltage, though, re-reading my old post reminded me that it does seem to read low compared to my multimeter IIRC which means that "low 12s" was probably a bad description and "mid 12s" is probably more accurate. I think this is the SG's own inaccuracy, though, not a PCM reported measurement -- the SG will report voltage even when the car's off which makes me think it's measuring it internally from the OBD2 port power.

As to the trickle charger, I know I really should just buy one. It would be useful in general since we have an extra vehicle that just sits most of the time and only get driven every 3 weeks or so.

I'm guessing it can't be too bad for a battery to start it out this way given that 99% of the population will do just that. I was just expecting it to be fully charged after 10 miles or driving or so and wanted to get a reality check on that.

To be fair, I don't *know* that it's not fully charged. All I'm basing this on is the voltage readings I'm seeing and I really don't know what exactly the system uses to determine when it should drop into its "reduce charging" state.

 

[The_Jeff]

For all we know Toyota's "eco mode" where the PCM demands a lower running voltage gets interrupted when it sees a battery disconnect, so it keept itself at a higher voltage for a few days.

 

[Torino]

Originally Posted By: 440Magnum
Don't trust a scan gauge for tenths of a volt accuracy. Use a real voltmeter.

What you're seeing sounds normal to me, EXCEPT you should NEVER see the voltage drop "to the low 12s" at any time while the engine is running. That indicates a problem with the charging system... assuming that the voltage is really doing that and its not just inaccuracy of the PCM voltage measurement reflected by the scan gauge. +++1

 

[Vikas]

Reading this makes me *glad* that Ultra-Gauge does NOT report battery voltage! I would be worried sick too

- Vikas

 

[wrcsixeight]

Flooded lead acid batteries will self discharge 12 to 15% per month at 75 degrees F.

Squeezing the last 20% into a battery is difficult and takes a long time, and voltages up to 14.4 to force the amps into it. A trickle charger is best applied to a battery which has been fully charged by a charger with the capability of bringing the battery to 14.4 volts. Most trickle chargers (under 2 amps) cannot bring a battery to the mid 14's and never really fully charge the battery.

Battery voltage should be measured at the battery terminals. The scan gauge, if it is reading accurately, has another couple dozen feet of thin wiring over multiple connections which equates to voltage drop.

In vehicles, the manufacturer's shoot for safety over rapid battery recharging and maximum battery longevity. The voltage regulators drop the voltage early to make sure the battery is not overcharged. An overcharged battery can get low on water, meaning more hydrogen gas within the case. Add spark, go boom.

Everybody overestimated the alternator's ability to recharge the battery. A 140 amp alternator can only produce that when cold, turning over 9k rpm, and have devices requiring that much amperage over wiring that can support that much current.
To fully charge a battery which required a jumpstart will take a minimum of 4 hours highway driving, and more likely double that. Always charge such a battery with a plug in charger, or the battery is destined to fail early due to chronic undercharging.

An alternator requires 1 engine HP to produce 25 amps. It is not free electricity.

 

[UNC017]

Originally Posted By: wrcsixeight
Flooded lead acid batteries will self discharge 12 to 15% per month at 75 degrees F.

Squeezing the last 20% into a battery is difficult and takes a long time, and voltages up to 14.4 to force the amps into it. A trickle charger is best applied to a battery which has been fully charged by a charger with the capability of bringing the battery to 14.4 volts. Most trickle chargers (under 2 amps) cannot bring a battery to the mid 14's and never really fully charge the battery.


There's also the whole issue of cell equalization. If a battery is kept on a "float" charger for a very long time, the cells can sulphate at different rates and while they all produce the same voltage, some cells may be in a lower state of actual charge. Running up to over 14 volts for a while is an "equalizing" charge which clears some of the sulphation and brings the cells back into uniformity.

Originally Posted By: wrcsixeight

An alternator requires 1 engine HP to produce 25 amps. It is not free electricity.


I think you're off by about a factor of 2 there. 25 amps times 13.5 volts is 337 watts, which is less than 1/2 horsepower (one horsepower = 746 watts.) Even if the alternator is only 80% efficient (they're typically more like 90%) then you're still only talking 420 watts of power taken from the engine, or about 0.56 horsepower.

 

[wrcsixeight]

Equalization voltages are in the 15.0 range.

As per the 1 hp to produce 25 amps I won't argue with math, But

Source

 

[Eddie]

I always put a new battery on a slow charger for about 10 hours depending on voltage.

 

[oilboy123]

This tells about the 1 hp per amps discussion:
http://www.arcomarine.com/xhtml/Tech marine charging systems.pdf

I always tell people who get jumps they need to use a charger later or the battery will take forever to charge. They don't seem like they take it to heart. I told it to my niece when I gave her a jump. Mostly for the reason that I was not going to give her jumps as a habit........

 

[RoadRaceJosh]

Wait, isn't this car only 3 years old? Why was the battery replaced? I have a 10 year old Dodge pickup and I just this last month replaced the original battery. I know I got lucky on that one, but 3 years is generally only 1/2 the life span of a car battery. My bet is that nothing is wrong with the car (nor was anything wrong with the original battery) and that the low voltage reading can be directly attributed to a load like the engine cooling fan. With the lack of good information about the vehicle and the test procedure there isn't much more to say.

 

[rationull]

Wow, thanks for the detailed information -- makes more sense to me now. Going on a longer drive in a couple days, hopefully that'll finish off the charge.

Originally Posted By: Joshua_Skinner
Wait, isn't this car only 3 years old? Why was the battery replaced? I have a 10 year old Dodge pickup and I just this last month replaced the original battery. I know I got lucky on that one, but 3 years is generally only 1/2 the life span of a car battery. My bet is that nothing is wrong with the car (nor was anything wrong with the original battery) and that the low voltage reading can be directly attributed to a load like the engine cooling fan. With the lack of good information about the vehicle and the test procedure there isn't much more to say.


From what I've heard the quality of OEM batteries on Hondas and lots of other cars these days can be hit or miss. I didn't replace the battery because of any of my own voltage readings -- it failed a load test. Given winter is coming and I've got some drives to colder regions coming up I wanted to get the jump on it.

 

[SteveSRT8]

Alternator output peaks at a MUCH lower rpm than quoted above. Shaft RPM does differ a bit from engine, but it's still not 9 grand to peak output!

And most cars will charge the battery hard and fast to over 90%, as they don't know when you'll need the battery again.

Also voltage required varies widely by temp.

 

[UNC017]

Originally Posted By: Joshua_Skinner
Wait, isn't this car only 3 years old? Why was the battery replaced? I have a 10 year old Dodge pickup and I just this last month replaced the original battery. I know I got lucky on that one, but 3 years is generally only 1/2 the life span of a car battery. My bet is that nothing is wrong with the car (nor was anything wrong with the original battery) and that the low voltage reading can be directly attributed to a load like the engine cooling fan. With the lack of good information about the vehicle and the test procedure there isn't much more to say.


Ah, there's the difference between where you live and where I live. Hot climates eat batteries for lunch- I've NEVER had an OEM battery last more than about 3 years, and even the best replacement batteries are doing good to survive 5-6 years. And I'm meticulous enough to add distilled water and keep them from running dry, but it just doesn't matter. When the underhood temperatures pass 200F battery life just goes away. Which is why so many cars now have the batteries in the trunk or mounted way down low in the engine compartment.