Can anyone help please. My boat has a 1 year old deep-cycle battery
which my 5hp Mariner outboard doesn't seem to charge any more. On
tickover it engine shows 6V and at high revs shows aound 10-11V. My
local outboard repair shop changed the rectifier and charged me £90,
but this hasn't made any difference - they say the output voltage is
not relevant, only the current - which shows 5A.

I thought the output voltage would need to be around 14V to charge the
battery. Is the regulator at fault ? Any thoughts appreciated thanks.