Well since the M5 almost ruined Leica pretty much rules out taking it seriously for so many people those of us who use M5's are automatically written off. So be warned.
My M5 has two things you won't find on most if any others. First and foremost is the full modern frameline set. Not impossible to do by any means, Sherry managed it quite nicely. Next is a modified Tom A Rapidgrip. Makes the "elephantine size and weight" a non-issue.
The M5 is one of my 'daily' cameras, one of the ones I carry with me always- and it never fails to be a pleasing piece to use. The shutter speed dial is wonderful, easy to knowledgeably adjust without having to remove the eye from the VF- the analog readout at the bottom tells you the speed selected. Metering is also nice when one wants to skew the reading- after a few days of shooting you will know how far over or under you are by the relationship of the lines in the readout. More information in that VF than any other M, yet it is in no way cluttered or distracting and has no red lights.
As to the ungainly size so many seem to gripe about- the M5 is smaller than most SLR's, much smaller than the SLR's of that vintage I've seen & used. Downright petite next to a D300 or an F5. Is it bigger than an M3? Yep. But so is an M6TTL.
To the OP: I use the modern 625 battery, and had Sherry make the adjustments for it after I found the Wein cells to be too expensive for the life I got out of them.