A common solution is to install a tricolour. This is of course also useful generally, but can also function if the bow navigations lights fail. While not legal
motoring it is probably safer than battery
operated lights that may not meet the required visibility standards and are difficult to fix in a spot with the correct angular cut outs.
With a separate house and start battery
you have a reasonable backup for the electricity supply, but an emergency
battery, mounted high above the waterline, is worth considering. It can also supply the VHF
and maybe GPS
A good selection of torches/flashlights is the final line of defence. Some models have diffusers that will transform them into an all round white light.
In the "good old days" many boats traveled offshore
with no lights or a single
white light. With the low power consumption
of LEDs there is no excuse for this, but there are more important backups that I would prioritise first.
All of this does not help if you have to legally carry a totally independent alternative, but if your choice is not hampered by having to comply with regulations
I think a tricolour is a better option.