Measuring current with a multimeter - What did I do wrong?
You placed an ammeter in parallel to a voltage supply, which created a short circuit through the meter and most likely blew the 10A fuse in the ammeter socket.

What you want to do is put the meter between the charger and the battery, and then connect the other end of the battery to the charger.  Diagram will help:







simulate this circuit &ndash; Schematic created using CircuitLab

Edit: If everything still works fine, it's likely you tripped some kind of over-current protection in the charger before the fuse in the meter blew.