Convert 48V battery bank to 12V for boat appliances - Inefficient?
Here's the item you linked: -




It's a 12V output capable of supplying up to 25 A - is this enough for your appliances
You can power it from 36 V to 75 V - is this OK for your set-up - Any unforeseen voltage spikes that might mean you need to consider over-voltage protection feeding the supply to it?
Efficiency of 94.5% means probably 90% if you read the small print but still this means that if you take about 300 W out (12 V x 25 A) you can expect to have to provide 333 W in and this means about 7 A taken from your batteries (48 V). As battery voltage drops to possibly 42V you can expect to have to provide almost 8A.


I have used one of these and it did the job. I also powered it from 48V. 

Each battery (wired in series) provides the same current and so the Ah rating stays at 100 Ah but obviously the current draw is significantly less when using a switcher. At full load (12 V x 25 A), I would estimate that this will work for about 11 hours before the batteries need a recharge.