Answer
Jul 22, 2025 - 08:57 AM
That red battery light usually means the charging system isn’t working properly. If it only comes on after running at high RPM for a few minutes, it could be a sign of:
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Voltage regulator/rectifier failure – Common issue on outboards. They can overheat and cut out after a while.
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Loose or corroded battery terminals or ground wires – Check all the charging connections, especially from the stator to the regulator, and then to the battery.
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Bad battery – Even new ones can be faulty. A failing battery might hold voltage at idle but can't keep up once the alternator kicks in.
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Stator or alternator coil issue – Less common, but if the stator windings are damaged, it might charge erratically or drop out under load.
If you’ve got a multimeter, check the voltage at the battery terminals. With the engine running at around 3,000 RPM, it should read about 13.5 to 14.5 volts. If it’s lower, your charging system’s likely to blame.
In any case, the outboard service manual should have full testing procedures and wiring diagrams if you want to dive deeper. Feel free to let us know more details about your BF90 (e.g., model year, serial number, etc.) so we can point you in the right direction.
