The other is that I don't recall, DC to DC going DOWN in voltage - usually it is to up step the volts and I don't think it behaves at all like an AC transformer - but I am about a meter beyond the bounds of my good knowledge. I think you will also find that once the 48 volt battery drops below a certain level, the converter (or regulator as I think it might be) is going to simply cut off, not getting out the last X% of amp hours.
Theoretically, yes. However other characteristics are affected. The 48 volt battery will probably have a maximum "cranking current" quite a bit higher than the converter.
Also, the conversion does not occur with 100% efficiency. Indeed, the efficiency depends on the load. Have a look at this high quality DC to DC converter graph of efficiency vs. load http://electronicdesign.com/site-files/e... You can see that at low power it is very inefficient and as load increases it gets very close to 100%. So depending on load, *this particular* converter would be a battery equivalent to 40 to 78 amp hour rating.
Crudely speaking, yes. This would be called a "buck" converter, and if you get a good one, it should be 90% efficient. I've seen 96% efficiency in our lab, but that's by spending an inordinate amount of money - not likely in a consumer product. So think of it as a 12-volt battery with a 72 AH rating. And if the battery bank is lead acid, drawing out more than half that amount will ruin the batteries.
If your converter was 100% efficient, in principle that would be right. In practice they are usually 75% - 85% efficient, so at a guess you might get the equivalent of a 64Ah 12V battery.
The benefit of the DC-Dc converter is that most of them will work with a fairly wide range of input voltages. This means you will have a stable 12V output even when the battery voltage drops near the end of charge.
If I install a step down DC to DC (48 to 12 volts) converter on a 48 volt battery with a 20 amp hour rating, will I then have a battery equivalent to a 12 volt battery with a 80 amp hour rating?
