battery dimensioning basics....

[andsarkit]

If you want to get a definitive measurement for any 12v consumer on board then one of these from amazon is worth its weight in gold ...

https://www.amazon.co.uk/dp/B093P64J13/

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I connected one in line with my fridge and left it running for 7 days then divided the total power used by 7 to get the daily usage for my battery and solar budget calculations.

I also had a BD35 based fridge but the amount of stuff you have in it, the quality of the insulation, the ambient temperature, and your preferred fridge temperature will affect the power consumption - which is why I measured mine.

It came out at around 0,6 kWh per day which was the biggest consumer on board by far. This equates to around 50Ah a day - so your 80Ah battery seems a bit undersized to run a fridge permanently IMO.

+1 for these.
I got one when I installed a small Chinese fridge and the consumption came out at 20Ah a day but I really need to run it for a longer period and in some hot weather for a true measurement. My 110Ah battery should last about 3 days but a little solar will extend that quite a lot.
It is also useful for autopilot measurement or anything that has an intermittent current draw.

 

[B27]

+1 for these.
I got one when I installed a small Chinese fridge and the consumption came out at 20Ah a day but I really need to run it for a longer period and in some hot weather for a true measurement. My 110Ah battery should last about 3 days but a little solar will extend that quite a lot.
It is also useful for autopilot measurement or anything that has an intermittent current draw.

Out of interest, can you share anything about the autopilot consumption?

 

[MontyMariner]

Do you tend to want to sit at anchor for a week without running the engine, or do you manage to sail long trips with no engine?

For me, Yes to both. I have 3x110ah house battery and 2x80w solar. Which is enough to see me across Biscay or sit at anchor for several days depending on how much sun there is.

 

[andsarkit]

Out of interest, can you share anything about the autopilot consumption?

Sorry I haven't measured that yet as I have fitted a Windpilot and only use the electric autopilot for short periods. I expect consumption will be very dependent on sea conditions and how hard the autopilot is working.

 

[Stemar]

Do you tend to want to sit at anchor for a week without running the engine, or do you manage to sail long trips with no engine?

Once you have enough solar to fill the gaps between engine use, the need for lots of battery capacity can almost go away.
At least on a minimalist boat with no inverters and thrusters and all that.

But OTOH, batteries are not really expensive in the scheme of things, if an extra couple of 110Ah batteries gives you a better Summer holiday with less stress, it's a bargain. Might even pay for itself in saved mooring fees?

Being a good Yorkshireman, I'm allergic to marina fees on the S coast.

Besides, we both prefer a quiet anchorage, and will happily spend several days without moving if the spot's right and the weather's right.