Well here I go again, this is gonna be a long post this time.
The battery light is coming on again in my 2004 X-Type.
In the fall after I bought the car, the battery light came on almost every time. So a 'new' rebuilt Alternator was installed, actually 2 of them, the first one didn't seem to work right, the second one, which I'm sure is my original one rebuilt, seemed ok, for a while. It started coming on again not as frequently but it did after only a week or so, and typically only after short drives. As the alternator had been done I bought a new positive battery cable after reading some posts here about the cable causing a resistance and therefore voltage drop across the cable. I bought the cable that goes from the battery to the starter and then to the alternator. But it hasn't been replaced yet as it's winter and I live in Canada and it's turned out not to be the quick job I though as you can't reach the Alternator nut easily. Even so I measured my current cable and have no resistance drop on the lead, so I left it for now. However, looking at the other +'ve cable in the car, the one that bolts onto the main cable and goes to the fuse box. It looks a bit more worn, so if there's an issue with the cable(s) I'm thinking it might be that one, but I can't tell how it connects into the fuse box, and it seems there is a wire off it that goes directly into the cable bundle that feeds into the car, so a new one of this cable looks to me like it would need to be spliced into the cable bundle and i'm not sure how it connects to the fuse box. So for now neither cable has been replaced, but when measured there is no resistance on either cable when I measure Ohms with my meter on the cables. The battery light has been coming on more frequently again now, typically a few minutes after the car is started. If it doesn't come on I can force it to buy turning on both the front and rear window heaters, or the rear and the heated seat etc. A few days ago I decided to replace another link in the chain, I bought a new $150 battery (I found out the old battery had a crack in the case and the green dot was not visible), I put in the new one and the same thing happened, so out came the new battery, I put it on my charger once I got home, it was at 50%, I charged it to 100%, put it in and no battery light that day at all, woo hoo I think. The next day after a couple of short drives, bingo on it comes again. Good Grief. So I now drive around with my Code Reader-Autel Maxitrip TP100 plugged in so I can watch the Voltage, which is typically in the 14-15 V range, after driving for awhile, it goes down to 12.5 or so. So it looks like the alternator is doing it's job, the new battery appears to be fine, I measure no resistance on either positive battery lead. So what the heck is going on. If I don't force the issue by loading the electrics, the light typically comes on a minute or so after I start the car and the voltage on my Scan tool is still in the 14 V range when it comes on. Well that's the whole story, bit of a mystery at this point.
Thanks for reading my long winded story.

Cheers
Dave

 

I highly recommend changing the battery cables. The cable that hooks up to the alternator is not that difficult to hook up as long as you can get under the front end via a floor jack. You might not be seeing a "resistance" in your cables when you are trying to measure them but it makes since that after a while of driving the cables them self heat up and that will increase the resistance within the cables. Often times they are corroded from the inside out and most often times not at the cable ends. I had this problem as soon as i bought my car replaced both cables and all was taken care of. The cables cost nearly as much as a new battery but my battery was still good and not the culprit.