Ford Focus 1.8TDCi 56 plate. So the car starts and runs fine. I got in it today and there's a whine from the engine bay think its around the Altenator/auxiliary belt pulley area. Check with the wife and she says "Oh yeah it's been there a couple of days" I do the dashboard trick thingy and it displaying DTC#01 9318 which I'm find out means Low Battery Voltage. Everything off the battery output show 11.8. If I turn everything on lights etc excluding the engine drops to 10.5. Engine on its 12.1 but if I rev/drive it it goes up 13 to 14. Looking online I'm just getting confused. Can anybody shed any light on this please?

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theres a connector which connects to the alternator, take that off while the car is running and retest the voltages, what are they?

also get the battery load tested at a garage as you have low voltage without the car running

Sounds like the alternator to me. With the engine running the batter should be showing in the region of 14 volts at idle.

it depends if the battery is the wrong spec or faulty the smart charge detects this and fails to put out the normal voltage so a free test at a garage is the way to go it may be the alternator there is a fuse for the smart charge in the engine bay fusebox from the alternator worth checking that

if the battery is dead and not accepting a charge the smart charge will switch off and revert to a normal alternator thats because the smart charge can detect voltage feed back since this can damage the ecu the alt switches to a normal one to prevent damage so it doesnt mean its the alt a proper chewck will save you spending money on parts you may not need and ide ask ford as most garages dont understand smart charge at the best of times

Okay thanks the help so far I been to Halfords to have a test done and the results are Battery test: Volts 12.32v Measured 328 EN(A) Rating 700 EN(A) Replace Battery advised. Starter test: Cranking 10.06v Time 1.28 secs Cranking normal. Charging Test: No Load 14.28v Loaded 11.75v Low output. So should I still retake the readings myself with the smart charge disconnected. Also forgot to mention earlier that I did let the battery run flat a fortnight back could it be it hasn't regained its full potential since then? Cheers again guys

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Another update I've been out tonight and I've disconnected the smart charge from the alternator and I'm getting pretty much the same results 11.9 engine off and 13.5ish under revs with all electrics off drops to 12.5ish with them all off. I currently have the battery out of the car charging it over night. To see if that helps any. Again any advise would be greatly appreciated

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Battery charged I'm idling at 14v ish driving at about the same with a few electronics and everything on about 12.5v is this good or?

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Thats about right yes so its not an Alt issue if the battery goes flat again its just not holding charge