Replaced battery as car would not start. New battery discharges itself overnight and car still won't start. Car has been in Workshop for 3 days and they say battery is perfect. They have charged it and say all aspects of battery are good. Car will still not start and they don't know why. Has anybody got any ideas.

https://www.askmehelpdesk.com/cars-trucks/when-asking-about-your-vehicle-303903.html

Perform the tests below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-11.html#post2123675

Check out the charging system:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-10.html#post1973613

If the battery is discharging overnight I believe that is called a parasitic drain
http://www.ehow.com/how_2249402_find-parasitic-battery-drain.html

Will the car start at all before the battery drains down? If not is it turning over or just clicking or doing nothing.

I have little to offer here but based on my experiences I would suspect a light staying on that you may not have noticed.
My pickup wouldn't start one morning and the battery was several years old (some warranty left-not much) so I went in and had it tested (major retail store) and it tested bad and they gave me a new battery with a slight discount.
I installed it and forgot about it and the next day-same thing-dead battery. I took it back-they tested-said it was borderline and gave me a new battery, which I installed.
I went on an errand (in daylight), stopped at a signal and happened to glance up and noticed that a dome light was on?
Then I realized what was killing the batteries. The light stayed on--drained the battery so I wouldn't see the dim light if any in darkness in the garage.
I had done a test like the one linked by Zemuss (but I think it used a voltage measurement instead of amps) and the test did indicate a parasitic drain but I didn't stumble into it until later on.

Car is Peugeot 406 Dsl.HDI, 75,000 miles.Tests by electronic&Peugeot engineers found no faults or drains. 2new batteries in 6 weeks still same problem To start car have to disconnect battery o/night.Could it be related to low overnight temperatures.

Did you test the charging system? Is the battery the proper size, especially in terms of CCA? Diesel engines are tough on batteries, especially in winter. Are you using full synthetic heavy duty diesel oil in your engine? Diesels start easier with synthetics, which also help save your battery and starter motor.

On my 2ltr hdi 2001,the problem was the cigarette lighter.Removed fuse and drain stopped.

Pinky,

This question has been dormant for a little over two years now. It is best to check the date on the last response sometimes before answering questions here.
It would be nice if questioners would let us know when problems are resolved or if they just decide to work around it and forget it - or give us some closure. But in my experience here so far, they rarely do.
It would be very beneficial for all of us if they would stop back and tell us how their problems came out in the end. It would help us provide better answers over time as we learned what the real problems had turned out to be as it added to the knowledge base. And newer folks researching the older questions would get much better information and maybe solve their own problem without even having to post a new question.
But, unfortunately that is just not how human nature usually pans out. I'll get off my soapbox and crawl back in my cave now. Lol