If a fuel pump goes faulty the battery can go flat if it continues to feed with no engine running. Fuel pumps are designed to work from 12-volt electrical system or within the range of 12 volts at the engine runs. A fault relay or an electrical short on the other hand, can keep the pump powered up even when the engine is turned off and in doing so be draining power from your car battery continuously. If unchecked, this can eventually lead to a completely flat battery and the car won't start next time you need to use it.
The battery is likely being drained by the fuel pump when the vehicle has been parked for an extended time and you notice a significant drop in battery voltage. As a result, drivers may experience hard starts or the battery may stay consistently low because they frequently need to jump start the engine or the they will have to recharge it using an external source. Continuous drain can sap 10-15% of the battery overnight depending on the power requirements of the pump, or complete discharge it in a few days if left unanswered.
Most of the time, the power is being drained by an issue with electricity, sometimes a bad relay or maybe wiring problems. If the relay is old or damaged, it may not be able to break the circuit and cause the pump to continue siphoning power while not powered at all Corroded or damaged wiring on the other hand, will cause a short and thus constant power flow. Photo: GOCF Regular checking of fuel pump wiring and relays, e.g. as part of a battery drain monitoring program at 60,000 miles, could go a long way in preventing any surprises on battery charge...
While replacing a worn fuel pump relay is a little cheaper than replacing your battery once it has been drained by the fuel pump itself that all adds to an unnecessary expense. As auto pioneer Henry Ford said, “To do more for the world than the world does for you — that is success. Ensuring such cases are addressed before they become worse, enables both the battery and Fuel Pump work effectively that is essential in minimizing tear and wear while maintaining a consistent performance of your car.