For some reason the anti robot anti spam filter keeps flagging my posts with more than one link :h
So, I will add..
For laptops, you can buy a "universal" laptop charger which can operate directly for 12V battery and some offer both 120V and 12V capability. The ouptut is universal meaning by just changing the tip to one that fits your laptop the voltage and amperage is set correctly for your laptop. Looks like this..
That is the one my DD has been using on a Dell two in one laptop with a i7 processor, has worked well on 120v and 12V.
Can be found
HEREThe more low power items you can run directly from the battery the better off you are, running those items through any 120V inverter then back to 5V or 18-19V for laptop wastes a lot of your RV battery capacity.
Some items, just cannot avoid using an inverter, most TVs the 120V power supplies are built into the device as well as sat receivers.
As far as trying to figure out your power needs from the wattage listed on devices goes, you most likely will way over estimate your power needs. Electrical devices in order to get certifications from UL or CSA they must list the absolute max power draw rating. Most devices will draw considerably less than what the name plate says.
Because of this, to get a more accurate reading one must monitor the actual power draw. One such device is called a "Kill-O-watt"..
