... the "repaired battery that won't ever reach 100% charge" bug.
I've just finished attacking a convoy where I had my stern batteries damaged due to depth charging. It took a long time, but it was finally repaired. Then when surfaced, I got the message that the batteries were fully charged, and the indicator light turned off!
On an unrelated note, what do the pics shaded in pink mean? This is a pic of the crew screen when the engine room crew were still repairing the damage caused by the depth charge attack.