Battery charging: How much driving after start?

[tc1446]

The batteries on the Accord and Slingshot read right at 12.4 amps after sitting overnight. My charger is an old one that can
be set to 2, 10, or Maintainer along with the hours. Should I "top" off these batteries, and if so, at what amp and for how long?

 

[eljefino]

Originally Posted By: Jetronic

I think you'll find this is done to get the most MPG: charging voltage goes up when braking or coasting, or if the SOC drops low, and drops when accelerating


Probably also keeps the battery from boiling out in texas heat. My MIL kept the OE battery in her lesabre, under the rear seat, for 12 years, and the OE battery in my HHR trunk is 10 years old.

 

[eljefino]

Originally Posted By: tc1446
The batteries on the Accord and Slingshot read right at 12.4 amps after sitting overnight. My charger is an old one that can
be set to 2, 10, or Maintainer along with the hours. Should I "top" off these batteries, and if so, at what amp and for how long?


Put it on on 10 amp mode and you'll see the ammeter climb to 6-8 amps then settle down to around 2. Also monitor voltage at the terminals; don't let it get over 15.2 or so.

A typical battery is 80 amp-hours, if it's only 90% charged you need to stuff 8 amps in in one hour but more realistically 2 amps over 4 hours. But the higher internal resistance of being nearly fully charged means the charger won't be delivering all it's rated for, which is actually a good thing. So short answer, 10 amp mode for four hours with you keeping your eye on it.

 

[SilverSnake]

Originally Posted By: blupupher
Originally Posted By: Ethan1
It's not recommended to put your battery on a charger every month. That's preposterous.

Topping off the battery monthly with a charger will give a lot of life to a battery.


Absolutely. And using a quality smart charger IS recommended by many high end auto manufacturers. In fact, many provide CTEK chargers with the car as standard or optional equipment.

http://smartercharger.com/

 

[SHOZ]

I have one of those plug in volt meters and it takes my Accent about a half hour for the voltage to drop below 14v from 14.5v peak.

 

[wrcsixeight]

The 12v receptacle will not read the same as a voltmeter placed directly on battery terminals, as there are likely many shared electrical loads present on the circuit which powers the 12v port into which you have your digital voltmeter. But it is certainly better than NO voltmeter, or an analog dash gauge in which one cannot discern a difference between 12.8 and 14 without a microscope.

The voltage indicated does not indicate state of charge, only what the vehicle's voltage regulator is doing as it was programmed to do, possibly with inputs as to battery or ambient temperature and amperage into battery.

My voltage regulator inside engine computer would seek 14.9v after starting and then choose 13.7 in a few minutes, then occassionally jump in between the two when driving.

14.9v on a fully charged battery is too high, 13.7v on an undercharged battery is too low to accomplish much charging while driving.

Now I choose 14.7 or 13.6 and an Ammeter tells me which to choose. If it is accepting more than 0.4 amps at 14.7, not fully charged and I hold 14.7, if it does, 13.6.

i will adjust up or down with battery temperature extremes

 

[circuitsmith]

I don't drive to work, so typically 2-3 15-60 minute drives a week.
Every 3 months I bring the battery into my basement, which is 60-70F, and charge it.
~12 hours on an adjustable power supply set to 14.5V, then a 1 hour equalizing charge at 15.5V
My last battery was going strong at 9 years old, but I didn't trust it for a 10th winter.
I do check with a hygrometer.

 

[901Memphis]

Originally Posted By: circuitsmith
I don't drive to work, so typically 2-3 15-60 minute drives a week.
Every 3 months I bring the battery into my basement, which is 60-70F, and charge it.
~12 hours on an adjustable power supply set to 14.5V, then a 1 hour equalizing charge at 15.5V
My last battery was going strong at 9 years old, but I didn't trust it for a 10th winter.
I do check with a hygrometer.



Why do you use 14.5V instead of 14.7?

 

[JHZR2]

Originally Posted By: Ducked
Originally Posted By: Ethan1
It's not recommended to put your battery on a charger every month. That's preposterous.

They might not recommend it, because they know people wouldn't do it, so it'd [censored]-off the punters and so be bad commercial practice.

That doesn't mean it isn't good maintenance practice.


+1

 

[Smokescreen]

All of my batteries are original and came with the car from the factory. When started they go at least for a 40 minute highway drive to go anywhere. All are as strong as new and never given any issues. 8,12 & 14 years old.

I put a CTEK charger on them once a year just to desulphate and do a complete charge.

When I lived in the city for 10 years, I went through 3 batteries on a different car. Short trips kill batteries worse than cold or hot weather ever will.

 

[circuitsmith]

Originally Posted By: 901Memphis
Why do you use 14.5V instead of 14.7?


I just do. Flooded lead acid batts aren't precision devices.
Variations in room temp would probably call for something else.
At any rate the batt ends up in much better state-of-charge than otherwise;
and lasts long enough.

 

[slybunda]

seen some cars that have the battery covered in an insulation type of jacket. is that worth doing? im guessing it keeps the battery warmer in winter?

 

[eljefino]

It mostly keeps it colder in summer-- heat speeds up the chemical reactions that wreck batteries from the inside out.

I guess they guess you'll do a lot of 15 minute drives and there won't be heat soak.

 

[SubLGT]

Originally Posted By: wrcsixeight
...Note that most batteries are not fully charged when the engine is started and most vehicle charging systems on their own will not really be able to accomplish a true 100% state of charge...


This is especially true on vehicles with BMS (battery management system). They undercharge the battery to save on the fuel required to run the alternator. Battery life is sacrificed for better fuel economy.

 

[Patman]

Originally Posted By: SilverSnake


Absolutely. And using a quality smart charger IS recommended by many high end auto manufacturers. In fact, many provide CTEK chargers with the car as standard or optional equipment.

http://smartercharger.com/


Yep, one of the options on my 2018 Corvette is a CTEK battery tender, and there is a handy plug in the hatch to plug it into. GM recommends using the tender whenever you're not going to be driving the car for a few days.

 

[bbhero]

Well stated blupupher.

Great information on here from Linctex, SilverSnake, wrcsixeight, and memphis909.

 

[DoubleWasp]

I have a lot of ProMariner Prosport chargers running around, due to my business. I've put them on batteries after long drives, and still had it take all night to fully charge the battery. Alternator are great battery maintainers, but awful battery chargers.

 

[bbhero]

Alternators ar even worse chargers now that fuel economy is given priority over charging/maintaining the battery. I got my Schumacher Sp3 out the other day to charge a battery I had just bought. It said it was 95% when I first hooked it up. It only took 15 minutes to say it was fully charged. Well, let's just say I unplugged the charger and repeated the process 3 more times in the next several hours. I did not trust that green light.