maxhunter17

SM3 Electric Auxiliary Battery Error

I'm pulling my hair out. I've got a 2017 Renault SM3, the electric one, and it's throwing some nasty errors. The speedometer keeps flashing a battery malfunction error, and when I hooked it up to a reader, it's storing a persistent error about low voltage in the auxiliary system. Starting the car has become a struggle, like the battery is super weak. It's got 139458 km on the clock. I'm seeing other weird electrical stuff happening too, like the interior lights flickering sometimes. I'm guessing it's related to the auxiliary battery not charging properly? Is this a common issue? Any ideas before I'm forced to take her to the mechanic?

4 comment(s)

I've seen similar issues in electric vehicles. The symptoms you're describing strongly suggest a problem with the auxiliary battery or its charging circuit. The auxiliary battery is responsible for powering the car's electronics when the main battery is not active, for example during startup or when the car is off. If it's failing, it can definitely cause those errors and starting problems. First, have you checked the voltage of the auxiliary battery itself? It should be around 12.6V when fully charged. If it's significantly lower, that's a clear sign it's not holding a charge. Also check the charging circuit; look for corroded connections, loose wires, or damaged fuses related to the auxiliary battery charging system.

Thanks for the quick reply! I haven't checked the voltage directly yet, honestly not sure where to even find the auxiliary battery in this thing. Is it usually under the hood like in a regular car, or tucked away somewhere else? And where would I find the fuse for the auxiliary battery? Is there a specific fuse box location I should be looking at?

Given the symptoms, it's almost certainly the auxiliary battery itself. While it might be tempting to try a DIY fix, diagnosing electrical issues in modern EVs can be tricky. Incorrect voltage measurements or short circuits during testing can damage sensitive electronic components. Also, the auxiliary battery in the SM3 is located under the rear seat and not easily accessible. Given the error codes and symptoms, I'd strongly recommend taking it to a workshop that specializes in electric vehicles. They'll have the diagnostic tools and expertise to pinpoint the exact problem and replace the battery safely. It sounds like you need a new auxiliary battery and that would cost you about 290€.

Thanks so much for the advice! I was really hoping to avoid the workshop, but it sounds like that's the safest bet. I'll take it to a local shop I know that works on EVs. I appreciate you confirming my suspicions, at least I'll go in knowing what to expect. Turns out you were right, the shop confirmed the auxiliary battery was shot. Replaced it, and all errors are gone. Cost me 290€ as you predicted.

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