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Consequently, I was engrossed in Fiona Bruce's Antiques Roadshow on my phone yesterday night when the MB app sent me a notification about a low 12v battery alert. So, the car hasn't been sitting dormant for a while and has had a good run since I just got back from Portsmouth on Friday.
I tried taking it for a run earlier, and it started up without a hitch on the first press. They checked the battery after I drove it approximately 20 miles, so I knew it was in fine shape. I take it to my regular repair shop for all my maintenance needs. Is it simply the car's electronics and software causing it to send out a false message that has no meaning? Does anyone else have this?
Everything looks OK, so my mechanic urged me to disregard it.
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12v Alert for Low Power
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LiamTheGreat
- Posts: 79
- Joined: Mon Feb 02, 2026 8:35 pm
Acquire a reasonably priced electrical multimeter and verify the battery voltage when the engine is turned off. The instrument cluster menu of my previous vehicle actually showed the battery voltage when the ignition was in acc (off) mode. As an alternative, you may purchase one of them for less than 10 pounds.
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LiamTheGreat
- Posts: 79
- Joined: Mon Feb 02, 2026 8:35 pm
As a quick answer, there's no need to bring the car to the shop if the battery voltage readings are within the normal range; the app must be mistaken.
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ThomasWhited
- Posts: 42
- Joined: Mon Feb 02, 2026 8:42 pm
Verify that the 12V battery status reads "charged" instead of "partially charged" in the app's "service" settings. The second option will render the car's stop/start feature inoperable. Even though it may have appeared OK right after the 20-mile run you described, a weak battery can see a slight reduction in voltage after some time spent standing.
Even though our 2019 C300 started up just fine, this problem rendered the stop/start function inoperable. The battery was replaced as part of the warranty and is still working perfectly after nearly 6 years.
Even though our 2019 C300 started up just fine, this problem rendered the stop/start function inoperable. The battery was replaced as part of the warranty and is still working perfectly after nearly 6 years.
For a more accurate reading of the battery's remaining life, you should remove it from the device and let it rest for at least six hours before doing a voltage test. Since a single defective battery in a bank of three or four might disable the entire solar power system, this is something we perform frequently at the marina with the leisure batteries.
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davejacobs
- Posts: 29
- Joined: Mon Feb 02, 2026 8:34 pm
Not only in the app, but also on the dash, you could see the 12V Low Battery Voltage warning.
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ThomasWhited
- Posts: 42
- Joined: Mon Feb 02, 2026 8:42 pm
After that, I'd be surprised if it wasn't just the battery. Even while they can endure far longer, in most cases they don't, the original one should be around for another seven years.
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David_Collyer1981
- Posts: 26
- Joined: Mon Feb 02, 2026 8:44 pm
I would receive such alerts because my automobile isn't used frequently these days, and when it is, it's typically for shorter trips.
Your companion will be the Ctek charger
Your companion will be the Ctek charger
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davejacobs
- Posts: 29
- Joined: Mon Feb 02, 2026 8:34 pm
If this happens more frequently, I will replace the battery, but I am assuming it is the original one.