Advice before I start...

[Powellct]

2004 206cc 1.6, running fine Friday (daughter uses it). Sunday we're on our way down to the O2 and get a phone call from daughter saying battery is flat. Late back last night so couldn't do anything. Checking this morning "economic mode" is showing which I gather it will on a low battery. She claims not to have left anything on (I can be a bit of tyrant if I think she's done something stupid - my bad), but I can't understand why or what would have drained it in 36 hours. Battery looks newish, but no proof. Drivers door can be a bit of a slam, so don't know if she didn't shut/lock it right - but a 5w interior light would end up with a dead flat battery - or would it? (5w = .4A/36 hrs = 14aH. Maybe not......)
Comments? Being a bit old school I'm guessing I can't just disconnect the earth and measure any drain, as I assume BSI, alarm, whatever else will all pull 12v. As far as I'm aware, no faults showing, but will know more when battery back up.

Ta,
Col.

[IanL]

First, you must observe the special procedure if you are disconnecting/reconnecting the battery. BSI reboot procedure.

It may be that the alternator is not charging the battery. The battery should show about 12.5V with the engine stopped, and about 14.5 with it running.

[Powellct]

Thanks Ian.
The first is entrenched, the second is a given once I get the bugger going. She's normally pretty good at telling me if lights come on - and its unusual (although I have had it) for an alt to fail with no light.

[Powellct]

Battery charged, nothing erroneous showing on display although I did have to reset the clock, starts runs fine. Most odd. Guess thats one of those "see how it goes" jobs.

[IanL]

Could be a combination of things.

Battery capacity reduced due to age, lots of short runs not putting enough back to replace the starting energy, something left on, a partial short due to gunge somewhere in the electrics (check in BSI, engine compt. fusebox, etc).....

[Powellct]

I'm pretty sure I know the answer to this as per my original post - but is there actually any way of checking for a significant drain? The only other way I can think of is a shunt and an ammeter, which I do have combined with my dwell meter (Google it if you're too young) - but I'd need to know what current everything else drains.

[Powellct]

......not to mention the hassle of the whole disconnect/reconnect process to get the shunt in....

[IanL]

I don't know another way of measuring. My guess is anything of the order of 0.1A or more would signify a problem.