Unusual fault code on DF150

Hi all. On a few ocassions now I get a short double beep imediately after the long start beep before engine start. The motor starts and runs every time and appart from this fault code I do not have any other issues. I cannot find this fault code listed in the motor manual. Any ideas? I am leaning towards possible low voltage (battery issue)? It seems to happen towards the end of a day out on the water where I will have bait pumps radios and sounder running all day. To get the fault code to repeat I need to actually start the engine, stop it and go for a restart. The motor and batteries are 2010 vintage. All ideas are welcome. Thanks guys.

Cheers
Craig

Yo man! You have it figured out. A battery with a higher reserve capacity will correct the fault. Thanks Martin

Thanks Martin
That's good to know on 2 counts. 1) my diagnostics were on the right track and 2) that the problem is of a minor nature.
Thanks again and you all have a merry christmas.