Your iron will work.
Make sure the iron tip is clean and tinned.
Place the tip on the battery connector.
Place a little solder on the iron tip so the solder makes a bridge between the tip and the connector.
Then wait.
The solder bridge will help to conduct heat to the battery connector.
The battery connector is a big lump of metal and it conduct heat away from the tip.
So for the solder to work you must heat a large part of the connector.
Place the tip of the solder on the connector and eventually it will melt.
Make sure the iron tip is clean and tinned.
Place the tip on the battery connector.
Place a little solder on the iron tip so the solder makes a bridge between the tip and the connector.
Then wait.
The solder bridge will help to conduct heat to the battery connector.
The battery connector is a big lump of metal and it conduct heat away from the tip.
So for the solder to work you must heat a large part of the connector.
Place the tip of the solder on the connector and eventually it will melt.