Absorbent Glass Mat (AGM) 12V batteries are used in GM Electric Vehicles (EVs), including the 2017-2023 Bolt EV; 2022-2023 Bolt EUV; 2023-2024 LYRIQ (Fig. 4) and HUMMER EV, due to their light weight, long life and maintenance-free design. The 12V system is used to power various control modules, electrical accessories, the instrument cluster and infotainment system, and other low-voltage components, which are not powered by the high-voltage propulsion battery.
Fig. 4
AGM batteries are similar to lead acid flooded batteries, except they use glass mats that absorb electrolytes that are pressed between the plates instead of immersing the plates in electrolytes, allowing for a smaller, lighter battery with the same amount of power that is less susceptible to heat.
High-Voltage Battery State of Charge
The high-voltage battery in EVs provides maintenance of the vehicle’s 12V battery as long as the high-voltage battery is above 10% state of charge (SOC). Dealerships should ensure the high-voltage battery system is kept above this level to maintain support of the 12V battery. The high-voltage battery should be fully charged to the factory pre-set charge level prior to completing the PDI.
EVs on the Battery Maintenance Report
An EV in the dealership’s new vehicle inventory will be added to their Battery Maintenance Report if the high-voltage battery SOC falls below 15% or the 12V battery SOC is below 50%. The EV will not be removed from the report until the high-voltage battery SOC is above 30% and the 12V battery SOC is above 65%.
When an EV appears on the Battery Maintenance Report, stating “Plug in High Voltage Charger,” GM recommends charging the high-voltage battery with a Level 2 or DC Fast Charger. All new EVs should have the high-voltage battery charged to 80% SOC upon receipt of the vehicle from the factory prior to PDI. The high-voltage system is designed to maintain the 12V battery SOC, but it may not prevent an unexpected large parasitic draw from depleting the 12V battery.
For more information about EVs on the Battery Maintenance Report, refer to Bulletin #22-NA-115.
– Thanks to Brett Holsworth and Marco Salcedo
