[RS3100]

It could be that the battery is low because of lack of use. All modern cars use a small battery current even when locked and parked to power the various control units on the vehicle, even though most are in a low power mode when parked. It might also be that the battery is old and could do with replacement, on a 2014 car. 6 to 8 years is about average for the life of a battery, although they can last a few years longer.

But the car has a smart alternator which charges more in certain driving conditions and less in others. Because of that, the battery is kept in a less than fully charged state to allow headroom to accept the charge from the alternator, and not waste it. But that does mean there is less room for the battery to lose charge and the low battery warning can be common, even with a very good battery, if for instance you are using the sounds system whilst parked with the engine not running.

Running the engine periodically for 15 minutes is one of the worse things you can do for the health of the engine. It will cause excessive wear over time. You would be much better off using a "smart" microprocessor controlled battery charger such as the Ctek devices, that can be left on for long periods of time with no risk of damaging the battery. Alternatively, the car would need a drive of around 30 miles or more to properly warm up the engine and burn off contaminants suspended in the oil. Running the engine for 15 minutes is also unlikely to put any appreciable charge into the battery, because you are probably using as much energy starting the car.

 

[RS3100]

I recently took it to a Volvo dealer and they checked it and told me that the issue is the battery is not a Volvo one so it could be that the issue is definitely the battery.

That sounds like a load of c066lers, unless it was a traditional old style lead acid battery, and not an AGM or EFB battery designed to be used on cars with Stop/Start systems. Such batteries don't have to be "Volvo" but it's always worth buying from a reputable make, rather than the cheaper mass produced batteries that are sold by online battery suppliers, relabelled by each supplier with their own or other unusual brand names . Those with a Volvo label on them aren't made by Volvo either. It might be that the battery wasn't programmed to the car when it was fitted, but if it was the same capacity and EFB or AGM it should be fine. There is a relatively small band of state of charge on these cars between the car being happy about the state of the battery and issuing the low battery message, due to the way that the system is programmed to keep the battery at less that a full state of charge. The system also averages the typical discharge rate over time, to predict future usage, so if you regularly use the radio whilst parked with the engine off, it will affect the appearance of the low battery warning, which may appear earlier than normal. That can be reset to the original baseline in VIDA though, if the estimated quiescent current use is higher than normal.

 

[RS3100]

The service book says that the belt was changed about 10,000 kilometers ago. Right now, the car doesn't show any errors since I started driving regularly, but the start-stop system is not working. The only thing left is to check the second battery, so I'll have to take the car to be tested, including that second battery, although it's difficult to access it.

Don't worry about the secondary battery unless you really really want stop/start. I have the system programmed out so it never works. But there are probably 30 or so reasons in the car handbook why stop/start won't always work. The secondary battery is only used to offload running consumers from the main battery for a matter of milliseconds when starting from a stop start event. It is recharged by the CEM (ECU) whilst driving, which normally takes a matter of seconds. At all other times, it is completely disconnected from the car's electrical system by a relay, also controlled by the CEM.

If you've been recharging the main battery, the BMS calculation of state of charge and the actual battery state of charge can get out of sync, and it needs time to recover. Normally 6-8 hours of leaving the car parked and all doors locked will sort that out, but there can be a lot of other reasons. As I say, mine's programmed so it doesn't work at all. My wife has just got a new car, not a Volvo, and there's no way to program it out apart from pressing the button every time you get in it, so it now has a small piuece of cable tie pushed down ther side of the start/stop button to keep it permanently off