BATTERY GONE

Hello,
i have a question about the battery of my citroen c3 1.4 hdi
I left my car stopped in garage for some months for problems to the engine radiator and fan,
(i have also another car).
Then i fixed these problems, and yesterday i used it all the day, regularly (i did some trips, i traveled about for 100 km in total)
And i leaved the car out in the night (not in the garage, as in the previous days).
Today morning i found the car with the battery almost completely discharged, so i was not able to start the engine.
Up to now, the battery did not have any problems, it was able always to start the engine.
I wonder why in a night it is dead.
I tried to recharge it for 7-8 hours but it reaches 11.8 volts (i tried it with the multimeter), it is too weak to start the engine.

Do you have any suggestion, some trick to bring back it to life?
What can be happened in the night to discharge completely the battery?

Thank you!!

I don't know about the battery drain but if a battery is really drained you need a big charger to attempt a recharge.

A 25 amp charger is the sort of size needed. You'll need to disconnect the battery from the car before charging.

Alternatively you could try battery reviver, tablets that go in the battery, these might make it possible to charge with a smaller charger.

If the battery still refuses to charge it's most likely replacement time.

Once you have a good, charged battery you can look at what's draining it.

Missing Lincs wrote:If the battery still refuses to charge it's most likely replacement time.

As Missing Lincs says, after you have tried to get it working again and failed, its time for a new battery. They are not designed to last forever and once they start to go down hill, its often more convenient to buy a new one, considering how reliant the car is on having a working battery.

You can follow this link for a new C3 battery (click here) from euro car parts, including free UK delivery

Thank you!
I have still a question:

The battery now is a BOSCH S4005 that is 60AH and 540 peak current
I wonder if i need 60AH or 55AH and 480 peak current is enought...

Thank you!

I'd check with a battery seller or Citroen or even your handbook to see what battery your car is designed for.

If the spec. says 60Ahr 540A then stick with that, diesels put a lot of demand on a battery when starting, especially in the winter.