The way that works Andy is the battery capacity is shown by in this case 40A, 7AH.
What it is saying is 40A cranking capacity.
Its continuous load is 7Ah ie 7 amps per hour. This doesen't mean it would be flat in 6 hours running 7A. It would be 'flat' long before that (actually at around 80% capacity serious damage is done, under 60% is critical). What it is saying is that the battery can continuously deliver 7A per hour, that is intended to work with a charging system putting approximately that back.
The 45A battery is capable of supplying more as cranking output but will be at a disadvantage in normal running. 4A may well be fine for this time of year but it wont last, it will work but as I said it wont last.
Normal daylight will be engine, ?
Brake light 21w
Sometimes indicators 42w
Total maybe 70W with some engine load. Or 6A Peak daytime.
Evening, as above but with what? 35w in the headlight that's 3A plus 5 for the tail and prob another 5 for the idiot lights/dials that's another amp with load. So your night time peak could be 10A certainly a continuous 5 or 6 allowing for losses can be expected. Explains the 7Ah.