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C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
OK to use battery maintainner with battery conneected?
Is it OK to use battery maintaier with battery conneected? This is for a 2002 C230.
I know itt's not good too connect a straight up charger, what about a battery maintainer?
Any specific recommendations?
I noticed in the MB manuals it will say to connect a battery charger of min 30amps while using a scan tool for diagnostics, so it seems ok to use.
I have a Noco Genius 5 I will hook up once in awhile for the "maintenance" its supposed to provide to batteries.
I have a W204 and removing the box above the battery is a pain so I instead hard wired the charging harness in. I connected positive directly to the battery post, I connected the ground to the chassis where the battery ground wire is connected. When I want to use the charger I fish the extension cord thru the grill and place the charger behind the headlight in the engine bay, this way I can close the hood.
From my research the ground should not be connected directly to the battery, it should be connected after the battery sensor monitor. I guess this way the cars computer sees whats going on.
Is it OK to use battery maintaier with battery conneected? This is for a 2002 C230.
I know itt's not good too connect a straight up charger, what about a battery maintainer?
Any specific recommendations?
The smartest charger + maintainer I know is CTEK perhaps followed by NOCO and more...
These chargers can maintain battery 24x7 while unused through Winter season.
If you prefer not to disconnect battery then do not use "AGM mode" setting while in circuit because charger supplies higher voltage (15.xV) to balance battery cells.
Use "regular mode" while battery is in circuit is great for AGM & floaded batts. Remember that stock batteries are vented outside.
Cheaper aftermarket batts may not be vented out.... hydrogen gas is HAZARDOUS near sparks
You may experiment to find that "REBOOTING" the whole car can be beneficial to sanitize sleepless modules gone-wild that drain battery while parked: SAM+CGW.
Some older chassis may loose memory settings of sunroof, seats, windows, radio code with power disconnected. The W212 holds all its settings.
Last edited by CaliBenzDriver; Dec 3, 2025 at 04:49 PM.
It only takes 2 minutes to unbolt the negative cable. Its prolly the best method to save a charged battery while sitting for a while. But like Caili said if your gonna use a battery tender get a good quality one. And there is always remote disconnects you can use too. Here's a couple examples.
Is it OK to use battery maintaier with battery conneected? This is for a 2002 C230.
I know itt's not good too connect a straight up charger, what about a battery maintainer?
Any specific recommendations?
Yes, a smart maintainer is fine to leave connected. It's designed for that. Just clip it directly to the battery terminals under the hood. The C230 doesn't have sensitive electronics that would mind. A simple CTEK or Battery Tender brand one works great.
It only takes 2 minutes to unbolt the negative cable. Its prolly the best method to save a charged battery while sitting for a while. But like Caili said if your gonna use a battery tender get a good quality one. And there is always remote disconnects you can use too. Here's a couple examples.
A remote battery disconnect switch is a great solution unless you have a battery sensor on the (-) side. It senses the core battery temperature by hugging the (-) post.
quick disconnect on the (-) side
With sensor mounted away it will sense cold battery....
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
Originally Posted by Alexie
Yes, a smart maintainer is fine to leave connected. It's designed for that. Just clip it directly to the battery terminals under the hood. The C230 doesn't have sensitive electronics that would mind. A simple CTEK or Battery Tender brand one works great.
...says the man who doesn;t even list what vehicles he has.
No sensitive electronics? Au contraire my good man. There's a very long thread dedicated to this very topic
in the W203 forum. And plenty of sensitive electronics. ECU EIS SAMS etc. https://mbworld.org/forums/c-class-w...g-battery.html
And just recently a thread I read where someone fried their front and rear SAM's from jump starting their car.
Supposedly.
So recently I bought a Schumaker 15/2 charger to replace my old 10 amp that finally died.
Wow, the Schumaker weighs nothing.
It says it's a maintainer, in the 2A setting. I'm reluctnat to use it though. It seems more of a dedicated charger.
I'd rather not connect and disconnect the battery as it rains a lot here and I'd rather not be messing with a 900CCA battery on a dark night in the rain. The car in question is a backup and the last time it sat for about 3 weeks, it took all day to charge the battery. I need it to be ready to go in a pinch. (262K mile C230 out to pasture so to speak)
There's a few good suggestions here, I'll check them out. Update your profile!
Last edited by C230 Sport Coup; Dec 6, 2025 at 05:16 AM.
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
Originally Posted by CaliBenzDriver
The smartest charger + maintainer I know is CTEK perhaps followed by NOCO and more...
These chargers can maintain battery 24x7 while unused through Winter season.
If you prefer not to disconnect battery then do not use "AGM mode" setting while in circuit because charger supplies higher voltage (15.xV) to balance battery cells.
Use "regular mode" while battery is in circuit is great for AGM & floaded batts. Remember that stock batteries are vented outside.
Cheaper aftermarket batts may not be vented out.... hydrogen gas is HAZARDOUS near sparks
You may experiment to find that "REBOOTING" the whole car can be beneficial to sanitize sleepless modules gone-wild that drain battery while parked: SAM+CGW.
Some older chassis may loose memory settings of sunroof, seats, windows, radio code with power disconnected. The W212 holds all its settings.
I'm not concerned witrh memory settings, Never had a problem with the radios.
W203 coupe does not have power seats. One less thing to break especially with the motoriized steering column.
So it's just a matter of resetting the windows, sunroof, and turmimg lock to lock 3 times.
I just ordered a straight disconnect same one listed here on amazon for $8. for now.
Still likely go dead sitting outside in the cold.
I almost ordered the NOCO Genius 2 but what I really want is for it to have a disconnect frpm the hard wired harness not mounted in the car.
Lots of cheaper ones on Amazon that do have that. and come with both clip and a hard wired harness.
Not sure if they can be trusted. Wife will be sure to complain about an extention cord running up the driveway
for long periods. Oh well.
Disconnecting battery(s) is a great way to stop "drain by parking" aggravations and benefit from "reboots" to help sanitize sleepless modules doing the busy drainage...
The power surge of starter crank is 800Amps.
See if "disconnect unit" is rated for automotive use... that means heat and vibrations.
it looks great with its remote clicker for single battery. For dual battery cars, disconnecting MAIN will drain smaller AUX to make up for missing power.
Last edited by CaliBenzDriver; Dec 6, 2025 at 01:43 PM.
My Noco Genius 5 seems to take 3hrs to do its thing before it goes into "Maintenance" mode. Most of those 3hrs the bulk charge is complete and its supposedly optimizing the battery whatever that is.
I originally bought the Genius 1 and that took over night to charge the battery it was slow. I then bought the Genius 5 because I got it for a really low price on Amazon "Used-like new". I will say if I already didnt have an ac/dc power supply I would have bought the genius 10 because that works as a power supply also.
I will hook it up if I havent driven the car on the highway for over a week or two. I mostly do short local driving around. Hook up the charger and let it do its thing until the green light is flashing and remove it from the car.
I bought the Ancel BM200 battery monitor awhile ago and used it to see what my battery was doing. Thats when I noticed how quickly the car charges the battery on its own. Even short trips it was charging fast.
My Noco Genius 5 seems to take 3hrs to do its thing before it goes into "Maintenance" mode. Most of those 3hrs the bulk charge is complete and its supposedly optimizing the battery whatever that is.
I originally bought the Genius 1 and that took over night to charge the battery it was slow. I then bought the Genius 5 because I got it for a really low price on Amazon "Used-like new". I will say if I already didnt have an ac/dc power supply I would have bought the genius 10 because that works as a power supply also.
I will hook it up if I havent driven the car on the highway for over a week or two. I mostly do short local driving around. Hook up the charger and let it do its thing until the green light is flashing and remove it from the car.
I bought the Ancel BM200 battery monitor awhile ago and used it to see what my battery was doing. Thats when I noticed how quickly the car charges the battery on its own. Even short trips it was charging fast.
"optimizing the battery" is balancing the cell voltage to reduce internal resistance. This is done by over volting cells under low current.... this is when lead-acid battery off gas hydrogen!
CTEK calls that cell-balancing "AGM Mode" to help regen batteries used in deep-cycles applications, usually AGM Batts.
It's best to follow all manufacturers recommendations (MB + VARTA + CTEK) to always disconnect Batt (-) side before charging and in particular the 15.xV "AGM-Mode".
These chassis are really voltage dependant ie. ALT + BATT in best shape. It's usually well worth the troubles.
Last edited by CaliBenzDriver; Dec 6, 2025 at 09:37 PM.
According to the MB manuals ive been reading thru in 2000 MB switched to AGM batteries.
The charging info I come across show using the charging/jumping terminals. On mine I hooked to the positive battery terminal connector because I couldnt figure out a way to hard wire it to the F32 jumper terminal.
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