Battery charging: How much driving after start?

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Hi,

Are there some general rules of thumb for:

When you start the engine, how many minutes do I need to drive the car in order to charge the battery to the charging state just before starting?

Lucas
 
It would be impossible to give you a simple answer like you want. Starting doesn't take that much energy from a large battery, it's running accessories while the vehicle is off that brings the state of charge down.

It takes multiple hours to get the battery from 80-100%

The alternator will never fully charge the battery because it will not seek a high enough voltage for long enough to bring the specific gravity to the proper full range.

It's recommended to charge your battery on the grid with a quality charger every so often when you can maybe once a month or so.
 
Too many variables for thumb. The Rat mostly has a dead battery, but it starts easily. I can jump it from the BMW and drive less than 2 miles to shop and it restarts? The alternator is putting out 14.5 v, I've checked that with a meter. The Bosch alternator on the 528e is set to only 14.1 V. It would likely need a jump. I keep a battery charger on the premises.
 
It depends on the voltage the vehicles voltage regulator allows, and how long it takes to crank the engine.

When my AGM battery is truly 100% charged, it accepts 0.0x amps at 14.7v

If I start my v8 engine at this 100% state of charge, when amps at 14.7v taper back to 0.0x, the battery is again fully charged.

This takes about 45 seconds on my vehicle.

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. It is best to use a plug in charging source to squeeze in those last few % which can take hours. The 100% charged lead acid battery is twice as happy as the 98% charged battery and will likely live twice as long.

Far too many people act like alternators defy the laws of physics, nearly instantly recharging batteries and are a 'free' energy source. They can't, Don't, and are not. Not even when chromed and polished and spoken to lovingly.
 
Originally Posted By: wrcsixeight


Far too many people act like alternators defy the laws of physics, nearly instantly recharging batteries and are a 'free' energy source. They can't, Don't, and are not. Not even when chromed and polished and spoken to lovingly.


Little known fact: This same law applies to women.
 
The emptier your battery, the faster it will return to the state it was before starting. Its internal resistance is less.

My gear reduction starter motor is rated for 1.5 hp which is about 1000 watts or 80 amps. So with a 100 amp alternator it'll theoretically fill back up within seconds.

If you do, say, a paper route, your battery will sink to about 75% state of charge but reach a "new normal" and not go lower as it's insanely easy to go from 74% back up to 75% after a start.

This isn't great for it as it will sulfate, so a nice long drive will get it to 95% and a shore power charge every six months would bring it to 100.
 
If you are concerned about the state of your battery in any vehicle, you need accurate information. I recommend the Midtronics PBT300. It will tell you the state of your battery in seconds both in terms of voltage and CCAs. I use mine to monitor the state of the batteries in my vehicles at least once per week. It will also easily test your charging and starting systems.

https://www.amazon.com/Midtronics-PBT300...ords=midtronics

If your driving habits are not keeping the batteries in your vehicles at the optimum level, then a good smart charger will take care of the problem. I use the CTEK Multi US 7002 although there are many satisfactory options. Simply hook up the charger overnight and in the morning your battery should be at the optimum level. Severely discharged batteries may take longer. A lot of car guys I know keep a CTEK hooked up to their cars any time they are not in use. This practice will make your batteries last longer than they would otherwise.

http://smartercharger.com/products/batterychargers/ctek-multi-us-7002/
 
With carburetors gone, most vehicles start right up and thus putting back into the battery what starting took out is done quickly. Obviously, headlights, defroster, heater fan may slow the process down. My pickup has a 1500w electric heater coil built into the heater system. I assume it consumes some power when it's on. For about 15 min after startup in cold weather.
 
It's not recommended to put your battery on a charger every month. That's preposterous.
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Originally Posted By: Ethan1
It's not recommended to put your battery on a charger every month. That's preposterous.
29.gif



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



I'd say at least a month if it's easy. If I had a garage with an outlet I'd be plugging up weekly
 
Would it hurt to have the battery maintained by the on-board smart charger on daily basis? I have my Tahoe rigged with on-shore power that supplies electric interior heater, seat heaters, block heater, oil pan heater, transmission heater and battery smart charger. Everything is controlled through three wifi timers. Smart charger gets power before anything else does, and I've made a habit to plug the power cord in whenever I park in the driveway. So it is natural for me to at least power the charger up. Am I doing a favor to the battery when I let it charge/maintain for 10-15 hours daily, or do I hurt something?
I'm really sorry for possibly hijacking the thread, but I couldn't rssist.
 
Originally Posted By: Ethan1
It's not recommended to put your battery on a charger every month. That's preposterous.
29.gif


Well, it was just recommended.
Topping off the battery monthly with a charger will give a lot of life to a battery.
 
Many people don't truly understand lead acid batteries.

No one here has even mentioned an "equalization charge" yet.......
 
I guess I can contribute to the subject as well. GM has some charging system in trucks like mine that is more advanced then many. It constantly monitors battery's SOC, and adjusts alternator output accordingly. So with my daily battery charging regime, the alternator produces 14.7 for about 4 minutes, up to the point that computer realizes that the battery is fully charged. Then the voltage drops to 12.6v, and could stay there for 30 minutes of driving, maybe more. Then it goes up to between 13.7-14.7. Then, after a while it drops back to 12.6V.
That is when the ambient temp is above 5C or so. When it is cold though, the voltage would never drop below 13.7V, and goes as high as 15V, so the software doesn't care about SOC, maybe it is trying to keep the battery warm? In any case, GM charging system would totally give you credit for the fully charged battery under normal conditions, and it will get it back to full charge quite fast after the start-up.
 
Google this: " lead acid equalization " and you'll learn car batteries never, ever, ever get to 100%
 
Originally Posted By: Donald
With carburetors gone, most vehicles start right up and thus putting back into the battery what starting took out is done quickly. Obviously, headlights, defroster, heater fan may slow the process down. My pickup has a 1500w electric heater coil built into the heater system. I assume it consumes some power when it's on. For about 15 min after startup in cold weather.


A carb doesn't change how easily a vehicle starts, it's the owners knowledge of the starting procedure.
 
Originally Posted By: yugrus
I guess I can contribute to the subject as well. GM has some charging system in trucks like mine that is more advanced then many. It constantly monitors battery's SOC, and adjusts alternator output accordingly. So with my daily battery charging regime, the alternator produces 14.7 for about 4 minutes, up to the point that computer realizes that the battery is fully charged. Then the voltage drops to 12.6v, and could stay there for 30 minutes of driving, maybe more. Then it goes up to between 13.7-14.7. Then, after a while it drops back to 12.6V.


Yep. Observed this anomaly on a 2016 GMC Sierra 5.3L with my Scanguage hooked up:

OjSvE35.jpg


With headlights on the alternator stays "on" as I was watching the voltage behavior when I was driving in the early morning and at sunrise. There is a ammeter looking device on the negative battery cable that measures current draw and the ECU uses that info to adjust alternator duty cycle.
 
Last edited:
Originally Posted By: yugrus
I guess I can contribute to the subject as well. GM has some charging system in trucks like mine that is more advanced then many. It constantly monitors battery's SOC, and adjusts alternator output accordingly. So with my daily battery charging regime, the alternator produces 14.7 for about 4 minutes, up to the point that computer realizes that the battery is fully charged. Then the voltage drops to 12.6v, and could stay there for 30 minutes of driving, maybe more. Then it goes up to between 13.7-14.7. Then, after a while it drops back to 12.6V.
That is when the ambient temp is above 5C or so. When it is cold though, the voltage would never drop below 13.7V, and goes as high as 15V, so the software doesn't care about SOC, maybe it is trying to keep the battery warm? In any case, GM charging system would totally give you credit for the fully charged battery under normal conditions, and it will get it back to full charge quite fast after the start-up.


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
 
Originally Posted By: Olas
Originally Posted By: Donald
With carburetors gone, most vehicles start right up and thus putting back into the battery what starting took out is done quickly. Obviously, headlights, defroster, heater fan may slow the process down. My pickup has a 1500w electric heater coil built into the heater system. I assume it consumes some power when it's on. For about 15 min after startup in cold weather.


A carb doesn't change how easily a vehicle starts, it's the owners knowledge of the starting procedure.


The starting procedure is easier on a FI car... And the FI calibration is more reliable than the carbs, over a much wider temperature range. Of course, not all carbs are created equal, but some are notorious for being finnicky and a change of weather can be enough to require another tune.
 
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