UK Electronics Repair Questions? Ask a Technician ASAP
Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, bear with us; re-confirm and post back with the complete model (number) of the "...am fm shortwave..." radio
The only easy user doable try would be to clean the battery contact of the radio and ensure that these contacts the battery terminals.
Other than the above, visually inspect the inside of the radio for any loose wiring and/or cold solder issues.
All others would require the use of a multi-meter and even perhaps a soldering iron.