Why does the battery on my mild hybrid keep going flat?
I have a Ford Puma 1.0 MHEV but have fault with 12 volt battery losing charge. It will run fine for two or three weeks but then will require jump start two or three times .Previously the car had a total breakdown which resulted in software upgrade then two weeks later a new coil pack fitted. Any advice?
Ross
Ross
Asked on 7 September 2025 by Ross carter
Answered by
Alan Ross
The 12V battery issue can stem from the mild hybrid system failing to adequately charge the 12V battery due to insufficient regenerative braking, potentially causing the battery to die and the car to stop working. Other possible causes include faulty hybrid battery connections from a past recall, general battery wear, or issues with the Battery Monitoring System (BMS).
The most common issue involves the mild hybrid system (which uses a 48V battery and an inductive motor) not generating enough power to charge the standard 12v battery for starting the car. Ford issued a recall for a specific period of 2020 models due to potentially improperly torqued hybrid battery connections that could lead to poor electrical connections and a fire risk.
Like any 12V battery, the one in your Ford Puma can eventually degrade and fail, particularly if subjected to heavy use or repeated deep discharges. Problems with the BMS( Battery Monitoring system ) can incorrectly read the battery's charge or state of health, leading to incorrect charging or a false indication of a dead battery.
The most common issue involves the mild hybrid system (which uses a 48V battery and an inductive motor) not generating enough power to charge the standard 12v battery for starting the car. Ford issued a recall for a specific period of 2020 models due to potentially improperly torqued hybrid battery connections that could lead to poor electrical connections and a fire risk.
Like any 12V battery, the one in your Ford Puma can eventually degrade and fail, particularly if subjected to heavy use or repeated deep discharges. Problems with the BMS( Battery Monitoring system ) can incorrectly read the battery's charge or state of health, leading to incorrect charging or a false indication of a dead battery.
Tags:
batteries
mild hybrids
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