I dont think ignoring it is a option
You are quite right it could be a knackered battery, though unlikely. (would expect around 12 volts when charging with a cell gone in the battery)
Most likely explanation is either lack of charging, or a high resistance in the wiring that supplies BOTH the items that read the low voltage.
for what its worth here is what i would do.
Firstly find out if the problem is with the supply to the instruments or the battery voltage really is low. do this with a digital voltmeter straight across the battery terminals, and check the difference between that reading and what your instruments tell you. if the battery voltage is normal then the wiring to the instruments is likely at fault.
If the battery voltage really is 10.5v then its likely its not charging.
with the engine running at a few thousand RPM the battery voltage should be between around 13v and 14.8v. if not then its likely its not charging and futher investigation is required.
check the charging connections, fuse if there is one, and check the stator continuity with the ohm setting on your meter.
If all that checks OK its likely the fault lies in the recifier/regulator packs. or the battery has a dead cell. Bench charge the battery for 2 days and leave stand for a day. Terminal voltasge should be well over 12 volts more like 13.2V 11.2 volts ish indicates a failed cell.
if the boat
cranks over fast on the starter and all else seems OK then i would suspect the wiring to the instruments or a dodgy battery first.
hope this helps