Late yesterday afternoon our Fireman neighbour, who I think I can almost now call a "friend"? knocked on my door. His wife's car, An elderly, 2nd generation, Kia Rio, won't start. Can I give them a jump? Aye, of course I can, but let's just do a couple of quick checks first. So, grabbing my Multimeter, We returned up the street to his house.
Ok, first off, what's the standing battery voltage? Approx 8 volts, that's not a good start. How long since it was last run? About 3 days but up to then it's been starting "fine". So lets just try a start and let me hear what's happening. Key turned and engine, very slowly, goes Wump, wump - two cylinders going over compression - and stops. Cranking voltage around 5 volts - I'm surprised it turned over at all!
Ok, so the battery is definitely "flat". Well yes, said he, I know that, so can you just give it a jump? (Wife needs to take the kids somewhere) Well, I could but with a battery showing these readings she may not be able to later restart it so they can come home! Oh, said he looking disappointed, but won't it charge up with the engine running? Maybe was my answer, but she's not going very far is she so unlikely enough charge will be achieved.
The battery itself is not the original and certainly doesn't look in it's first flush of youth either. Oh how I wish I had a battery condition analyser! Anyway, he started, quite politely, "leaning" on me to jump it. So, against my better judgement, I popped back to my house and got my big jump battery. Connected in the accepted way, ie. pos on my battery to pos on the Kia using the "red" lead, then and my battery's negative terminal to the cylinder head of the Kia using the "black" lead. But WOAH, as I touch the negative clamp to the head there's quite a spark! Don't like the look of that. Never a good thing is electric sparks! So I didn't continue but suggested we do a parasitic drain test first which would at least give us some idea if there was a serious short going on somewhere. He didn't have time for me to muck about as he decided to run the kids and wife to wherever it was they were going in his car and said he'd check in with me tomorrow to resume the task.
I went back to my garage with my big battery - that's a heavy thing to wander about the streets with - and to search for my ammeter - which I haven't used for many years (much safer to check stuff on voltage scales if possible so I avoid going near taking amperages wherever possible) and after turning out a load of "useful stuff" there it was at the back of the shelf I keep all my electrical gear on:
It's an old and "trusted" friend I acquired at the Portobello autojumble many years ago. I'm expecting to see the needle barely flicker when introduced in series with the battery and negative lead, ignition off, doors closed etc, of course. Let's hope there's not a massive short which will "kill" the meter. - Note to self, Must fit a fuse into one of the leads - As I was thinking about the prospect of a serious short and associated sparks etc that go with such things I was suddenly "hit" by a thunderbolt of a realization - Of course that earth lead sparked when you went to connect to the head, the vehicle battery is pretty much DEAD! and I was, in effect, connecting a fully charged battery (my big jump battery) directly across the vehicle's "dead" battery by doing so. There was likely a potential difference of around 6 volts going on here, Of course it sparked you numpty! By the way, for those less experience members reading this, that spark is why you never make the final earth connection to the battery negative terminal - batteries emit hydrogen and oxygen gasses, highly inflammable, BANG! - As all you "old lags" know I'm sure.
So, if, as I expect, I see no, or very little parasitic drain when I test later today (most probably) then I'm going to connect up my big jump battery and I'm confident I'll then be able to start the engine. I'll leave the jump battery connected while I check for battery voltage to see if the alternator is charging - expecting to see somewhere in the region of 13.5 to 14.5 volts. If this all checks out I'll let it run with the jump connected for 5 minutes or so to allow the duff battery and jump battery voltages to balance before disconnecting the jump battery and we'll take a drive down to Halfords where they, I know, will do a free battery condition check for us and, if needed, I can use my trade card to get him a good discount on a new battery.
I'm pretty confident that what we've got here is simply a failing battery with sulphated plates and unable to keep it's charge over any period of time. The standing voltage observed was around 8 volts and the engine very nearly cranked so I'm not worried about an internal short in the battery - I wouldn't be bothering to try any of this if battery voltage was very low or zero as it's pointless trying to "wake up" such a battery. However, at 8 volts, it might just be needing a good charge or it might be needing a new battery, The battery condition test should establish the answer to that question.
So now I've got a big smile on my face and hoping for a not too expensive outcome for my new friend.