Why does my M6 battery run down so fast?
Typically because you forgot to turn off the light meter.
With the meter still on and something pressing lightly against the shutter button (say in your camera bag), then the circuit will stay open and run down your battery really fast, in usually 8 hours for a fresh battery.
Versions of the M6 older than the TTL use the shutter dial "B" setting to turn the meter off. Some users remind themselves of this by associating "B" with "Bag" — when you put the camera away, set the shutter to "B" for "Bag".
The newer M6 TTLs have a separate "Off" option on the s/dial next to the B setting. Same thing, but easier to remember right?…
M6 TTL issues
One thing to note about the M6 TTL, putting the shutter on B is not enough to switch off the electronics. You must put the shutter to "Off" to kill all current drain! See the following LUG post with exact current draw figures:
At the above URL, John Collier concludes:
It is fine to leave the camera "on" as long as there is no pressure on the shutter release. If there is pressure on the shutter release and the camera is not "off", the battery will drain down regardless if the shutter is wound or released. If the camera is being carried in a case, it would be prudent to switch it to off; other than that, I would not worry too much. [ … ] Leica states that a new battery will give around eight hours of metering time so it would be easy to drain the battery overnight if there was pressure on the shutter release.
While on the subject of M6 TTL battery drain, in Nov 2001 Jeff Moore claimed the very early TTL models had a design fault which resulted in excessive battery drain:
[Problems with his brand-new 0.85 M6TTL…] It also had the early TTL problem of sucking batteries dry in weeks. I sent it in for repair, and waited with some frustration as it didn't come back, and didn't come back... then, a year later, they sent me a new camera.
Turned out they were waiting for the engineering team to redesign the electronics so's not to require bus-bars from a hydroelectric plant to keep 'em powered, and for the changes to make it into production. The new camera has been perfect — including battery life comparable to the M6 Classic. So... frustrating at the time, but I admire their insistence on getting it really truly right the second time.
(Back in 2001 I wrote to Mr Moore asking for details about this — specifically dates & serial numbers. Never got a reply.)
For a historic discussion of the battery drain characteristics of the M6 TTL,
see the following May 2000 thread on the Leica Forum:
On/Off switch on battery cover?
For all of you who keep forgetting to turn the s/speed dial to "B" or "OFF", in September 2002 Larry Welker started selling a M6 battery cover with a built-in on/off switch which he calls "The Rose". See the photos and details on his www site at <quickreleaseplate.com/m6switchpage.html>.
(N.B. Welker's site appears to have gone offline. According to <Photo.net: #00BumQ> his small factory burned down in October 2004. I'll keep the link in the FAQ in case it goes live again — AZN)
Securing the battery cover
Harrassed about the battery cover continually unscrewing and falling off? Use the coin-slot battery cover meant for the R! Just screw it in and tighten it up with a coin — this baby will now stay in place until Kingdom Come. The part number to order for the black chrome version is #442-299-805-009.
Another solution is to wrap a small amount of teflon packing tape onto the cover's screw thread before screwing down tight. This teflon tape is used by plumbers to seal screw-together piping and is easily available from any hardware store. It's also less messy (and easier to buy) than the green-coloured "adjustment holding Loctite" you see mentioned so frequently on US-based mailing lists.
A warning about Loctite
DO NOT EVER use the red "222 Super Screw Lock" version! Despite claims of "Low Strength" on the packaging, it's strong enough to bind your battery compartment so securely that you'll have to resort to pliers to wrench the thing off!
A note on batteries
BTW, I highly recommend you use 3V Lithium ("1/3 N") batteries as they have a ten-year shelf life and thus won't run down so fast while your camera is stowed away. Unlike Silver Oxide or Alkaline batteries, they also keep their voltage right to the end, so there's less chance of ruining rolls of film with slowly expiring batteries.
As of 2006, "1/3 N" lithium batteries are getting harder to find. Most camera stores don't stock them anymore (actual quote: "Wow, that's the smallest camera battery I've ever seen!"). Luckily you can still buy them however from any electronics supply store — in Sydney try David Reid Electronics, Jaycar or Dick Smith etc.
I wish I was kidding :?/