Remember I have not been able to establish the impedance of the nüvi 2495LMT speaker, only the one from the nüvi 2595LMT (4 ohm). From a point of standardisation across nüvi's not likely, but maybe the original speaker from the nüvi 2495LMT was 8 ohm too...

As for battery drain: if using an 8 ohm speaker instead of a 4 ohm speaker would only reduce the battery drain (but also reduce the volume output). Right?