Hybrid's Weak Start Points to Battery vs Sensor Battle

Had similar issues on a 2015 Buick LaCrosse Hybrid. The vehicle diagnostics initially pointed to battery health problems, but further testing revealed a malfunctioning voltage sensor. The symptoms matched exactly, slow cranking, dimming lights, and inconsistent battery voltage readings. The voltage sensor sends incorrect data to the power management system, making the car behave as if the battery charge is low even when it isnt. In my case, replacing just the battery wouldnt have solved the issue. The faulty sensor was causing the charging system to malfunction, which eventually could damage a new battery too. This was a serious problem that required immediate attention because it affects the entire hybrid power management system. The fix involved replacing the voltage sensor unit and recalibrating the battery monitoring system. After repair, all systems returned to normal function, no more slow starts or dimming lights. Given your symptoms, the mechanic is likely correct about the sensor. These issues are common in hybrid systems as they age, especially when approaching your mileage. Worth getting it properly fixed to avoid potential damage to other electrical components.

Thanks for confirming my suspicions about the voltage sensor. Since getting mine fixed, the car runs perfectly, normal starts and stable electrical system. Been about 6 months now with no issues. Curious though, what was your final repair cost? Mine was around €400 including parts and labor, but prices vary. Also, did you need any follow-up repairs or recalibration after the initial fix? The battery voltage readings took a few drive cycles to stabilize on my Regal GS.

Thanks for following up. The total repair came to 315€ for the battery sensor replacement and recalibration. The low voltage warnings disappeared after the fix, and the battery charge readings normalized within about 3-4 regular driving cycles. No additional repairs were needed after fixing the bad battery sensor. The power management system just needed those few drives to fully relearn and establish baseline readings. The mechanic explained this is normal behavior after sensor replacement. The investment was worth it, six months later, all systems continue working perfectly. No more slow starts, fluctuating voltage readings, or dimming lights. The repair addressed the root cause rather than just masking symptoms. Your experience matches what the service manual indicates about these systems needing a brief adaptation period. Once the new sensor was properly calibrated, the battery health monitoring became completely reliable again.

Thanks everyone for the input. Just wanted to share how my repair went. Took it to a different shop that specializes in hybrid systems. The mechanic first ran complete vehicle diagnostics which confirmed the voltage sensor issue. They replaced the sensor and did a full battery maintenance check. The entire job took about 2 hours. Final cost was €375 including parts and labor. The battery charge readings took a few days to stabilize completely, which they said was normal for the system to relearn. Really glad I got a second opinion instead of replacing the battery. Three months later and the car starts perfectly every time. No more dimming lights or weird voltage readings. Good lesson in finding the right shop that knows hybrid systems.