I suspect you have a converter, not an inverter. An inverter in an RV takes 12 volt DC power and turns it into 120 volt AC. A converter takes 120 volt AC and converts it to DC. Your equipment most likely will charge your
battery, but many of the older units are not very efficient. If you have a new battery an charge in incorrectly you will ruin the battery. The technology we have today is much better than it was 35 years ago.