I had the same problem.
And yes it was a battery thing (recharching up to 99%) and yes manually canceling auto-battery-charge really helped BUT...
it was not always the case. There were some cases were I felt that the problem was weather conditions. Making 10 kts with an opposing storm that lasts days isn't the same as making 10 kts in swimming pool conditions fuelwise, at least in Real Life!

Maybe this is also somehow included in the game engine (which would be a great

for the devs, by the way!).
Anyway, I got transfered to Fremantle and as the war progresses (now I'm in Spring '44) you also get some forward refueling posts, much closer to the action!
Life is so much easier when you're winning the war!