Flat car battery

[Barquentine]

I left my headlights on overnight. The battery is a couple of years old but still going strong. Now it's very flat after my blunder.
I connected the battery charger but the lights on that don't come on (neither the 'Power' nor the 'Full' light). They both come on when I disconnect it from the battery.
Is it the case that if a car battery goes completely flat then it can't be recharged?
For now I've left it connected to the charger in the hope the battery will revive. I've a vague notion I may have killed it though. Can anyone confirm my fears? Many thanks.

[gordyagusta]

Hard to say without testing the battery itself, however the lights dimming or going out on the charger when you connect it to the battery is not some thing to be concerned about, they should gradually come back on as the battery recharges...

[scotman]

Your battery should still be OK. Are you sure you have been connecting the charger the right way round?

[Barquentine]

I think so Scotman. Black lead to negative terminal and red to positive - the opposite to what I'd expect it to be since red singles danger which I associate with 'negative'. Pretty convoluted way to remember but it works for me...I hope?!

[MantaRay]

Keep the charger connected for a few hours and the battery should recover. Make sure there is nothing switched on in the vehicle which could be drawing more current than your battery charger is capable of supplying.

[Hymie]

Adding to the above posts – it is not advisable to charge a battery while it is connected in circuit on the vehicle. It is possible for the charger to damage the alternator diode pack and other voltage sensitive components.

If you are able to charge the battery without removing it from the vehicle – then it is advisable to disconnect at least one battery terminal from the vehicle circuit.

It is unlikely that you have caused irreparable damage to the battery by allowing it to be completely discharged – leave it charging overnight and see if it recovers.
Before giving up on the battery – borrow a more powerful charger, capable of at least a 6 amp charge.

[defenstrate]

dont forget to open the cells and ensure the battery fluids are at the correct level.

[Barquentine]

Many thanks for all your helpful answers. I've taken it out of the car and am leaving it on charge. I have a spare charger I'll try if this one doesn't charge it up. Thanks again to everyone.

[TonyV]

yow got your flat car started?

[KJN]

.....and remembered the radio code???

[Barquentine]

Thanks everyone. There was a fuse on he undersid of the charger which I replaced (30p!).
Battery now charged and car back on the road.
Thanks for everyone's advice.