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If I don't drive a car often, is it better to occassionally drive at a higher speed, but shorter time, or drive at a slower speed, but longer time to charge car battery?
Also, are both starter battery (under hood) AND auxiliary battery (in trunk) charged, or only the starter when you drive?
The alternator puts out the same charge (14+) whatever speed you are going. But, more time driving will provide a bigger overall charge.
Just buy a good trickle charger ( I prefer Ctek) and place it on your battery if your car sits idle. You will have a fully charged battery when you head out.
Yes, both batteries charge.
If I don't drive a car often, is it better to occassionally drive at a higher speed, but shorter time, or drive at a slower speed, but longer time to charge car battery?
Also, are both starter battery (under hood) AND auxiliary battery (in trunk) charged, or only the starter when you drive?
TIA
It is good for the car to be driven periodically at least once monthly regardless of the battery condition. A couple of times a month is even better but I know I myself don’t drive enough but once a month for sure.
Thank you both for the reply.
To clarify - after acquiring the used E350, I only drive the older old cars for short trips such as grocery runs, or in bad weather.
I do drive them at least once a week, but was just curious how best to maintain the battery health, as I'm told short trips don't really recharge them that much, as the amount required to start engine is much more than what's regained in short trips.
It's like going forward one step and backwards two steps, if that analogy makes sense...
Just trying to see if it makes sense to do a longer trip once a week/every two weeks/month, etc...
Trickle charger is a good idea, but I'd be constantly removing it & attaching it...
Here's a tip on how to tell the state of battery charge. This works well for me, but YMMV.
In my 2016, I leave the Comand system on all the time playing music from the SD card. Of course, when I turn off the engine, the music ceases when I open the door.
Next time I enter and start the car, if the battery has sufficient power, the Comand system and its music will start immediately, as expected. However, I've noticed that when battery charge drops low enough, Comand will NOT turn on automatically when starting the engine. I have to push the button to start Comand manually. I use this as my queue to connect a charger when returning home and shutting down the engine.
With the trickle charger you can just hook it up for a couple of days and then drive around for a couple weeks until you have a chance to hook it up again. Takes 2 minutes to connect/disconnect.
I am sure there are better more expensive options. But it this one works fine for my application.
It does not "continuously" but only charges then voltage drops below certain level.
Given recent posts in other threads on the topic, I am also not convinced that both batteries are charged from a single charger on the main battery.
Someone with access to MB systems posted to say it's inconclusive whether the two batteries operate on the same system and share charging.
I would like to get to the bottom of this, because while the main battery is easily accessed for charging, the trunk battery (or earlier dash battery) is not convenient at all.
I use a trickle charger and my Aux Battery had to be replaced on my W212.
The way I read his post was it charges both when driving... which is correct. Putting a trickle charger or maintainer on the main battery does not seem to charge the aux battery based on experience.
The way I read his post was it charges both when driving... which is correct. Putting a trickle charger or maintainer on the main battery does not seem to charge the aux battery based on experience.
Ah, thanks for the clarification. It makes sense that both batteries would get charged while driving.
While they do both get charged when the engine is on, it isn't hard to connect a set of SAE pigtails to each battery and leave said pigtail in an easily accessible spot (capped, of course) for ease of connecting a battery maintainer.
on my truck which only gets driven occasionally, I wired a pigtail to the battery with an SAE connector right where the bakc of hte hood and left fender meet with the bottom of hte windshield, and I plug a 10W solar battery tender into it when itss parked more than a couple weeks.
my tractor sits out in the field for months, so I permanently wired a 5W solar panel to it and tiewrapped it to the top of the frame for the front loader, keeps the battery fully charged.
of course, Solar isn't useful if you garage it. In which case a Battery Tender or small Noco or CTek would be the way to go. you only need one with a couple amp max output to maintain a battery thats already charged.
I agree, driving the car is the best way to charge the car battery but CTEK's trickle charger has proven to be reliable when I use it as well . It keeps the battery fresh and charged even after months of hibernation
I agree, driving the car is the best way to charge the car battery
beg to differ, but car alternators will try and dump as much current into a dead battery as fast as they can, and the battery would be much happier with a 6 or 10 amp smart charger, like a ctek, noco, batterytender, etc and a overnight charge cycle.
CTEK's trickle charger has proven to be reliable when I use it as well . It keeps the battery fresh and charged even after months of hibernation
yeah, ctek makes excellent charger/tenders. I've used Deltran Battery Tender stuff for some years and have a Noco 10 amp smart charger now that can also act as a tender, and that all has worked just fine for me over the years. My diesel truck has a 10 Watt Deltran Battery Tender brand solar panel hooked up when its parked for weeks/months. I should clean that truck out and take it for a drive, its been nearly a year, OMG.
Last edited by Left Coast Geek; 03-03-2021 at 02:29 AM.
The way I read his post was it charges both when driving... which is correct. Putting a trickle charger or maintainer on the main battery does not seem to charge the aux battery based on experience.
The Aux battery will not charge until the Power Relay tells it to charge, so using a trickle charger on the main won't keep your Aux battery charged.
The Power Relay looks at main battery voltage and aux battery voltage and has a timer that kicks in after about 15-20 minutes of driving, if the voltages meet requirements. That is what connects the Aux battery to the main battery for charging. So, if you don't drive the car, the aux battery will eventually go dead. Only way around that is to specifically charge the Aux battery itself.
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The Aux battery will not charge until the Power Relay tells it to charge, so using a trickle charger on the main won't keep your Aux battery charged.
The Power Relay looks at main battery voltage and aux battery voltage and has a timer that kicks in after about 15-20 minutes of driving, if the voltages meet requirements. That is what connects the Aux battery to the main battery for charging. So, if you don't drive the car, the aux battery will eventually go dead. Only way around that is to specifically charge the Aux battery itself.
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So, it does charge while driving.... if we are getting into the weeds, then we need to distinguish W212s with/without eco start/stop as the auxiliary battery function is very different.
Last edited by bmwpowere36m3; 03-03-2021 at 09:39 PM.
02-28-2021, 07:00 PM
Best way to charge car battery?
