Help me settle an argument...
 

So, my father and I have been having debating this issue of late.
He says that using accessories during short drives, as in less than 15 minutes, is a major drain on the battery and will decrease its lifespan. The suggested explanation is that things like seat heaters and rear-window defoggers use up more power than the alternator can recharge during the duration of a short outing.

I've been running these accessories on short drives for years, and have rarely had any battery issues, so I'm not 100% sold on the idea. For those of you out there who are more technically-minded or experience than me, is there any truth at all to his logic? Can running accessories on short drives negatively impact battery performance or lifespan in some way?

Thanks in advance!

Completely depends on what car you are asking about, condition of alternator, battery, cables, and what accessories you are running.

-alex

It generally takes between 5-10 minutes of the engine running to recharge the energy used to start the car. So in theory, he's probably correct about the ratio of energy drained vs energy regenerated when taking short trips. However, I can't see it decreasing the life of the battery unless you only take short trips, and no longer drives. One solid hour long drive can make up for power lost over a few short trips.

You are correct on all points. I have customers who only make short 5 minute trips in their cars, and end up needing a jump every month or so. I talk to them about trickle chargers, but what do I know? :iono:

Will you have an issue? Probably not, but your father is correct, over the long term, and when conditions are correct, it will have a negative effect on your battery.

Thanks for the info! So it sounds like he is right, at least partially. :thumbdown: :thumbdown: :lol:

I think I do enough longer driving mixed in with short trips to the train station that it isn't something I need to be actively concerned about...

If you let your car warm up for 5 minutes or so, which you ought to do in my opinion, then your alternator has the chance to regain some energy. There are a lot of premises in his argument that are pretty bold and aren't easily answered. But if we assume the car is new the battery is new etc etc, and depending how you drive and what accessories you use will determine if the battery is fighting a losing battle. I personally disagree because I had a POS stock battery in the charger I had before my brz and I ran an extremely complex and powerful sound/lighting system and my battery lasted 90k+ miles. I would go on more but I'm writing this during a class, hope this adds insight.

very easy to tell, use a volt meter( lighter,obd2) 14.2 is charging 13.6 is static
12 is discharging. if, during the short drive the voltage falls below 13 then the alternator is not producing enough power to run the extras and charge the battery. the first charge rate will be high then taper down.
harbor freight sells a very cheep plugin, red-yellow-green led indicator. (sold as an alternator checker)

My car sits all winter, drive it on the weekends and sometimes to work in the summer when its nice, the drive to work is about 6 mins.(i drive back home for lunch and back to work) Still have the factory battery and never put a tender on it. I do start it and let it warm up when it is really cold, which has not been really an issue this year in Ohio. - Bought car new Nov. 2013, 7100 miles on it now and battery seems fine.

He's your dad, just tell him he's right. lol

LOL. You came here to settle an argument?
I disagree with those that say you are draining a battery when the car is running. If everything is working properly then as soon as you start the car you are running on the power from the alternator not the battery. The battery just completes the circuit and receives a charge once running.

It is a little more complex than the arguments above.

When you crank the engine to start, the battery provides a lot of wattage for a few seconds.
Up to 100 Amps of cranking current @ 12V (12V*100A = 1200VA or ~1.2 kW). (disclaimer numbers are WAG - wild ass guesses)
If it takes 3 seconds to crank, then that is 3.6kWs of energy or 3600 Joules.

Of course the alternator carries the entire car's electrical load once the car is started AND recharges the battery.
But the battery will not accept a charge in 3 seconds like it took to discharge it, it has a charge current that depends on a lot of things like input voltage, temperature, and age of battery.

What is the charge rate of the battery right after starting? :iono:, but if it is 10 amps, then it should only take 36 seconds to recharge.
1 Amp of charge would need 360 seconds or 6 minutes.

Turning on all of the car's systems lowers the system voltage which will reduce the battery charge current, which would take longer than leaving all systems off.
This only has a small effect IF the alt. is running under capacity as the output will remain in regulation.

So - it depends.

My BRZ definitely did not like taking lots of short trips and it WOULD eventually drain the battery and not start. It was worse during the winter (cold battery = slower charge?).

I had to replace the POS OEM battery at 35k miles.
So your dad is right - Lots of very short trips means you are slowly draining the battery by not letting it fully recharge each time.
What is the length of time it takes to get the battery back up? :iono:
But turning on all of the car'e electrical systems right after starting COULD mean it will take longer to fully recharge.

You need your battery to be discharged and recharged. Lead acid batteries have a memory. They will begin to function at a level that corresponds to the demand placed on them. If you never use them to where they get drained somewhat, their capacity becomes diminished. On the aircraft I fly, we have to do some battery starts instead of always using a ground power source to start. Otherwise, battery starts become impossible as the battery won't get it done. This is on turbine engines with about a 30 second start time. All lead acid batteries are like this. It is important to pull them down and recharge them. Letting them Sit at a level of discharge like he is talking about will only be a problem if they are never charged back up, and you repeatedly try to use them to start the car when it doesn't have enough juice to actually start the car. What he is talking about just increases the amount of time to recharge the battery, as some of the alternator power is going to accessories and not to battery charging. Use your accessories, you'll be fine. Just make sure to drive a bit longer with some regularity in order to fully recharge the battery.

I've killed two batteries.
Both replaced under warranty, but the receipt/paperwork for the second time clearly stated "Car is not driven much or very far; trickle charger recommended". I drive 3 miles to work, on occasion. Speed academy just featured a good trickle charger.

We don't drive our vehicles far (short trips daily), so i connect them to a battery tender every month or so.