about a year ago I started getting low battery voltage alarms almost every time I turned off the car (voltage was always around 12.5V the next day) and the auto start/stop system stopped working, so I bought a new battery (it was 6 years old). I reset the low battery monitor and the start/stop started working intermittently. Soon after we started getting the low battery alarm again if I sat in the car with the radio on for more then a few minutes, and the start/stop stopped working. Every once and a while I would reset the low battery monitor and have the same results, things worked for a while then would stop. I was about to replace the low battery monitor but found it was part of the negative battery cable and was more then I really wanted to spend. A little more research and I found out that the Volvo ECM needs to be told when a new battery is installed, as the ECM controls the voltage differently for an old battery. So I found a 4 step reset to tell the ECM there is a new battery. 1. Ignition on engine off. 2 select dipped lights. 3.rear foglight switch on/off/on/off. 4. 4 way flasher switch on/off/on.. the battery icon will flash three times, it is now reset. Believe it or not it fixed it. Without doing anything else the start/stop started working the very next time I drove the car and has been working for about 2 weeks now. I sat in the car with the radio on for about 1/2 hour the other day and I did not get a low battery alarm. I find this very unusual that the car's ECM would control battery voltage differently for an old battery vs. a new battery, and how does it determine when a battery is old? next time I start having these symptoms i will simply reset the ECM and save the cost for a new battery, since my old battery wasn't showing any other signs it was bad.

 

Exactly what (main) battery did you put in? (part number, brand, size, etc)

And are you aware there is a second smaller aux battery hidden under the hood?

 

Got it from Advance Auto Parts best I can tell it's a DieHard Silver group size 615 CCA 76 204007 Part # 91-1. Yes I have been monitoring the Aux. battery, it was my first thought when the start/stop stopped working. it sits between 12.5-13 Volts with engine off and 14.5-14.9 with engine running

 

Yes, pretty much all new vehicles with BMS and AGM batteries need to know when the battery is replaced so that they can properly charge them. And if you replace it with a battery that has different specs from the original the BMS needs to know this as well so it can properly manage the charging. This doesn't mean that you have to use the OEM Volvo battery, but you should use one that is equivalent. Depending on how long you ran the new battery before letting the BMS know that it was replaced, you may have slightly reduced the life of the new battery by undercharging. AGM batteries are more sensitive to proper charging than old flooded lead acid batteries.

 

I don't know anything about cars other than driving it. What is BMS and how do we let it know that we replaced the battery?