question about batteries

tim1970 wrote:

So, what happens to the DC only things when I am plugged in to shore power? Do they continue to run off of battery, and then the shore power keeps the battery charged? Or is there a converter that will convert AC to DC when I am plugged in? If it is the former, then that tells me I always need a battery, whether I am plugged in or not. Correct?

If I am understanding everything correctly, I could bring a small generator (2000W) and be able to charge my batteries and be able to run my TV, built in stereo, or even the coffee maker or microwave (just not at the same time) Pretty much everything except the AC?

When connected to AC power, the converter supplies 12V power to the 12V system. On modern RVs, this is just connected in parallel with the battery and everything else, so the power from the converter can either operate 12V systems or charge the battery or do both at the same time.

I'd say it's generally a requirement to have a battery all the time, even when plugged into power. Some converters do not produce very clean 12V power and rely on the battery to act as a filter. Sometimes you may need or want to (temporarily) use more 12V power than the converter puts out, and the battery supplies the excess for the surge. On a trailer, you generally need to have a battery installed whenever towing because it operates the emergency breakaway braking system, which is required by law in many areas and is a very good idea everywhere.

Some really old converters had separate battery charge outputs and accessory use outputs, and included some built-in switching arrangement (either manual or automatic via a relay) to select battery power when not plugged in. That's ancient history now, and if you happen to get a unit with such a converter, would be very very well served to replace it with a more modern unit.