Hi tonight my 2005 s40 battery went flat at work. I tried to jump start it, the headlamps came on and all the interior lights lit up but the engine didn't turn over. It didn't even try to start. When I disconnected the jump leads I tried to lock the car but nothing happened so its still unlocked. Is it possible that the car has 'forgotten' the key fob? Or is the battery just so bad that it couldn't be jump started? Please suggest any fixes.
Thanks

 

Your battery is completely dead/bad. Consumer quality jumper cables are not going to start your car, they can't carry enough current.

How old is your battery?Can you take it out and recharge it with a battery charger or just replace it if it's 3-5 years old?"

 

I'm not sure how old the battery is I haven't had it for very long. My place of work is a few miles away its a good 90 minute walk each way and I don't fancy doing that carrying a car battery. So if I replace the battery I won't have an issue with the key fob or the immobilizer?

 

If the battery is why your car won't start or lock, everything will work normally after you simply replace the battery. The only thing to train or reprogram is usually the automatic up/down window function. Keep in mind the battery could have gone dead because the alternator is bad and not recharging the battery. Or very rarely there is a drain on the system where the battery is drained while sitting still, key out of car. If the alternator is bad, after you install a new battery the car will run until the battery is dead again. Simply connect your $5 volt-ohmeter and verify the voltage at the battery with the car running is 13.5 volts or so. A fully charged battery is about 12.5 volts so if the voltage in the system is lower than that with the engine running - the alternator is not recharging the battery.

 

Thanks for the information I'll give that a try.

 

also, when a battery goes completely flat, it takes time to put even a base charge into the battery to get enough juice to crank. Usually this is a death blow to the battery so its likely going to need a replacement. As hoonk noted, you can use your multi-meter to guess at how much charge is in the battery. check out: https://www.aa1car.com/library/2003/us20310.htm

 

Yes this covid thing has had a lot of other effects , not driving a car for a long time certainly more modern cars that always draw a bit will eventually drain it once drained and you try to start it will damage it , on old cars was simple just disconnect it , but newer cars need a small amount to run the electric etc and if flat need lots of things to be reset .
If you do use a more modern car then get a inteli charger and just charge it every 4th week , a normal charger may give problems as some of the electronic components if connected direct may get damaged
But end of the day its just a new battery and all should be fine

 

Battery has been replaced and everything works fine now, thanks everyone.

 

Glad to hear hopefully now with regular use you will have no more problems