My 855 has developed an intermittent battery drain fault, always overnight, seemingly when the rain comes down but it's also occurred once when dry. It'll be fine but when I return to the car in the AM it'll be flat. No lights left on, nothing obvious that might be drawing current. Once started, the battery will charge pretty quickly. The only indication that something is not right is the headlight bulb warning light will light for a short time after jump starting. It's left my good lady wife stranded twice now so need to restore confidence quickly. Anyone know of some action I can take.

Gratefully, Henry

alternator?

I am a bit puzzled as well, but have had odd occurances with other cars during rainy days.

There is a simple way of halting the problem temporarily, until you can locate the problem. They make various versions of a battery cutoff, which allows you to remove all positive power from the battery, either electrically (the simplest to use regularly, but most complicated to install, although not that bad), or the direct mechanical disconnect, which requires popping the hood to disconnect/reconnect the power (simplest to install, least user friendly). This can at least stop the drain during the night.

My first guess would be a bad/weak battery. Low water level possibly, but least likely (use distilled water though if you refill it). Batteries loose initial power when they cool down (not much but a weak battery can become problematic), and a the battery is at it's coolest over night it could be part of the problem, just as usually rainy days are also cooler, and will cool off the battery quicker as well.

Of course you may simply have a some bad electrical components that are draining power, but there are so many it is difficult to suggest where to start.

Out of curiosity do you have any aftermarket electric items? (stereo head unit, amplifier, navigation unit, etc). It is not uncommon for people to hook them up improperly which caues them to drain power while the vehicle is off instead of being turned off entirely while the vehicle is off. Alot of people will improperly hook up the +12V and Switched +12V wires, which can cause a slow drain.

Initially though, I would suggest taking the car to a local autoparts store that will do a complete battery check to verify the battery is good (repeated problemslike you say could caue the battery to go bad quicker anyways, even if the battery is not the problem but it can make the problem worse). Most such places will do a battery check for free.

Yeah, I was burying my head in the sand to avoid considering the 'A' word. It may have to be examined....thanks

Thanks, hadn't considered a cutoff. It seems like a good step regardless of drain problems as the car can stand for days at a time. It'd slow the less bright car theives as well...

There are no aftermarket bits at all - completely stock. I guess re-seating all connectors to headlights would be a start as there could be some shorting there.

The puzzling part, which has stopped me from replacing any parts as yet, is that the car is so consistently reliable/regular outside of these anomalies. It's almost metranomic - 2.5 turns and it fires. No argument.

Off to the battery shop.

Thanks for response, Henry

Keep in mind the battery disconnect will caue various issues as well, that like a dummy I completely forgot to mention.

1. You will have to enter your radio code to get the radio to work every time you reconnect the a battery disconnect.

2. Your car' computer will probably lose it's efficiency settings every time you do this as well, making it be slightly less fuel efficient for the first 10-20 miles until it recalibrates itself (repeating again everytime you disconnect it for more than 20 mins or so)

I dont know if it was standard on 850's, but many have the built in theft protection to keep the car from being able to be started if someone breaks in or trie to start the car in an abnormal manner.

Stupid question, have you had the battery checked?

After that the usual suspect is the glove box light switch, it's amazing how quickly an internal light or 2 can drain a battery :haha:

Do a search on here and you will find all kinds of advice like attaching multimeters and clamp meters to determin the current draw when all is switched off, then pulling fuses to determin which circuit the fault lies in.

Good luck :thumbsup:

good one big-ben, didn't even think of that one. good call.

Yup!

Glovebox light!
:)