Just changed the Start/Stop Aux battery in my 2020 XC40 Momentum and I discovered that with the ignition OFF there is no voltage to this battery. Evidently the only way this battery is hot is if the engine is running. I was trickle charging the main battery monthly since we have not been driving much lately assuming that is was also charging the Start/Stop Aux battery but I just learned that it isn’t. I was hoping to find out how to isolate this battery so I could charge it independently but I can’t follow the circuit. I do a lot of short trips so I suspect this new battery to fail in 1 1/2 years or so because of that. Anyone know how to charge this S/S battery exclusively ?

 

Sorry cannot help with how to charge the auxiliary battery. Stop/start on my 2019 XC40 almost never works. Again, very little mileage the past two years and recovered just a bit after recent trips. Dealer has been of no assistance.

 

While I was in there and had verified that the two batteries were not connected when engine was off I ran an additional wire from the positive terminal of the Aux battery up into the engine compartment so now I can monitor/charge that battery separately when desired.

 

Thanks for the info re the auxiliary battery.

 

My start/stop function has also not worked since the 2nd week after buying the car. I have a 2019 model and I've had both main and auxiliary batteries replaced, and the alternator swapped as well, but it continues to have electrical faults. It used to be that every year or so it would throw a "Charging fault, service urgent. Drive to workshop" or a "12V system service required" error, but now that the warranty has run out, it has begun draining its battery within days. I charged it to 100% with a Schumacher battery maintainer (using the AGM setting) but within 2 days, the battery was sitting at 30% charge (about 11.3V). I just replaced the main battery myself using instructional videos I found on YouTube, but honestly this is ridiculous. The Volvo manual calls for only 15mins of driving per week to preserve the battery and I drive 30mins PER DAY! There is no reason the battery should die this frequently. If anybody else out there is having the same problems, please consider joining this class action lawsuit investigation: https://chimicles.com/volvo-dead-bat...investigation/