An interesting question!
IMHO, any sewing machine, computerised or not, can be operated on battery power.
In order to avoid modifying the sewing machine an inverter (preferably pure sine wave) that converts the direct-current battery voltage (often 12 V in caravans and RVs) to 230 V alternating current is needed. Here is one example out of many:
https://www.offgridcamper.co.uk/product/12v-300w-pure-sine-wave-inverter/Non-industrial sewing machines are not very power hungry so an invertwer capable delivering of a couple of hundred Watts is more than enough. When the sewing machine is idle, it is only the lighting and electronics that consumes energy. If you have a machine with incandescent lighting it pays off to purchase a LED replacement lamp, which will lower the power consumption significantly.
Edit: Just for fun I checked the power draw of my Juki DX-7, which is labelled 230V/75W. At idle the power is 22 W and when sewing in six layers of ordinary cotton cloth at full speed, the power rises to 36 W. The label value, 75 W, is probably a value that may be reached when the machine is operated at its capacity limit. This is similar to the power consumption of an ordinary laptop PC.
/Michael