Stop/start service required
 

2016 XC90 D5

Got the dreaded “stop/start service required” last week so asked Volvo to investigate during my service. They advised auxiliary battery was dead (no readings) and main battery showed 65% SOC and that both would need to be replaced at a cost of over £500.
Does this sound right to you, both batteries going at the same time? It’s 7+ years old now so I half expected new main battery might be required but have hardly ever heard of both going? What’s strange is that very occasionally stop/start still works which I don’t think would be the case if the aux battery was dead. I think the dealer is going for the easy option of replacing both.
Any thoughts or tips? I’ll probably look into replacing them myself, any recommendations on what/where to buy?
Thanks.

Earlier this week I had the 'Support Battery Service Required' displyed a few times so had no Stop Start. I went and bought myself a smart charger. After 6 hours of charging no more information displays and normal service resumed.

Certainly not,,, put them on charge for as long as you can. The car must have been standing for a couple of years to get in that state if they were of course. The support battery has an easy life .

Thanks. The car is used regularly but pretty much exclusively for short journeys. I’ll get it on a charger and see how the batteries respond.

I think the Main Battery and the Support Battery get out of sync.
Charging through the single connecting point seems to sort it out but if not, disconnecting the main battery will make the Battery Monitor recalculate.

I replaced my support battery earlier in the year for the message 'Service Needed' with one from a Volvo dealer on line. It takes seconds to fit. But I also bought an intelligent charger that got rid of the message before I found the discounted battery.

On our previous S60 disconnecting the support battery for 5 minutes used to sort it out.
Our MX-5 also needs the battery disconnecting every now and then to get the stop start back.
I support 'OldEngineer', the 'computer' says NO so the old disconnect and reconnect is a cheap option to try, and it may just fix your problem.

Thanks for all of the advice.
After charging for 48 hours the issues persist and a quick check with a multimeter confirms that the support battery is dead. I’m therefore going to bite the bullet and replace both batteries. Seems relatively easy but I have a couple of questions please:
1. Are there any issues with disconnecting both batteries at the same time (I assume not as all key data is now hard stored unlike the “old” days)
2. I keep reading that the battery management system (BMS) needs to be reset to recognise the new batteries and optimise charging and battery care. Seems that a trip to Volvo is needed but are there any alternatives? I’ve heard that disconnecting both batteries and allowing the car to power down for at least 15minutes does the trick but feedback is patchy. Any experts or Volvo techs on here who can advise please?
Thanks again

Well you tried your best, just change the battery or batteries, the battery monitor will soon build up fresh data as time goes on.

I have a 2019 XC60 D4 in which the start/stop function hasn't worked for some time. I have borrowed a Noco Genius 5 battery charger but it has two modes...one that is labelled 12v and one which is labelled 12v AGM.

Which one should I use?

Use the 12V AGM mode. Don't connect the charger directly to the battery in the boot. You must use the charging terminals in the engine bay.