Yes, very odd, not something I've not tried before, and the spec does say 2.4 volts as mentioned by coromonadalix
The Brymen shows 2.9V. The spec sheet says 2V but also an open circuit voltage of <3.5V, so maybe it has something to do with being (effectively) open circuit?
I'm sure someone will come along and say we are doing it wrong
PS. Apologies for the grubby look of the 179, it's my 'outside' meter, and well used.