Why don't car batteries have a better state of charge indicator?

Renault? There's one which takes a mechanic 2-3 hours to change the headlight bulb. 5 devices have to come out first, including I think the alternator.

I asked a woman for a jump start once, fancy BMW or Merc or something. Took us 10 minutes to work out how to open the stupid battery cover. Why cover a battery? Did they think someone might steal it?

They're not sealed, there is still a vent, but you can't pour stuff in as it's at the end.

Have you ever seen what happens when you drop a tool on top of the battery?

Other manufacturers seem to get away with a simple clip-on, clip-off cover on the positive terminal.

True. And it is cheaper.

But once I saw BMW mechanics working on the cars dressed with white coveralls...

A teacher at my school in 1980 had a scarred face and bald patches amongst his pudding-basin haircut. When I got to know him quite well in the sixth form (I was a prefect whose duty was in the audio visual room that he was in charge of) he told me about the scars and the bald patches. He said that he had been working on his car about ten years previously and had accidentally dropped a spanner on the car battery. He remembers seeing it glow white hot and the next thing he remembers was waking up in hospital with bandages all over his head, and intense sores all over his face.

The battery had burst when the sulphuric acid boiled, and had sprayed boiling acid all over his head. Luckily he was wearing glasses which saved his eyesight. He took his glasses off and there was a very distinct line between smooth, unscarred skin round his eyes and red, scarred skin elsewhere.

He warned me not to be prat like he'd been. Also if I was jump starting a car, attach the red +ve jump lead first (to the +ve battery terminal) and the black -ve lead second to a convenient bit of metal on the engine, on the opposite side of the engine compartment. A flat battery gives off a lot of hydrogen and oxygen as it is being charged by the donor battery, and it makes sense to create a spark (by completing the circuit when the second lead is attached) as far away from the source of those gases as possible.

It's a while since I've looked at my car battery but I think the terminals are shrouded by raised plastic around three sides (apart from the side where the leads leave the terminals, and the leads are insulated to within that shrouded area. If a spanner falls on the battery, it will not be able to touch both terminals at the same time. Only a curved or C-shaped piece of metal could so that. So it looks as if manufacturers have learned from accidents like the teacher's and build in safeguards now.

The best one ever was a fork lift with a dying battery - the engine needed overhaul and it wasn't used much so the battery was always on charge and over charged.

Someone dropped a spanner and there was an almighty Fukushima level hydrogen explosion. Split the battery open and leaked acid all over the shop floor.

Merry days.

Why roughly? And unless the battery's royally f***ed, that should be an indicator of charge.

It is often possiable for one of the cells failing but the other cells can be good. Part of my job was to check around 100 batteries each month. I would check the voltage of each cell and the specific gravity of the liquid. I have seen one or two cells fail but the others were ok.

Because it is either the ball floats or not. Or two or three balls. Whereas a proper hydrometer as a graduation all the way from zero to a hundred. Analogical.

And then as it only measures one cell, it can be totally wrong. That cell may be good, but another three cells can be totally bad and you don't know.

Someone was on a ladder working near the open rack of the 48 V distributor at a mobile phone exchange. Some of the false floor tiles were also removed for access. He started to fall (bound to happen one day), he grabbed for support, but he had a screwdriver on his hand, and put it across the copper bars. And the screwdriver didn't have an insulation sleeve on the metal. Could be a wrench, it was long ago, but all the same, tools used at that location should be protected with a plastic sleeve and they were not.

The result was the whole area (an island) without mobile coverage for an hour or two.

The chap was mostly unharmed, but sent to hospital nonetheless. Stress or shock. Mental shock, I mean.

(I guess he released the tool sufficiently fast to not be burned, but it melted)

Surely the ball floats more or less depending on density of the acid. Imagine yourself floating in a lake. Now float in the sea, now float in the dead sea. The denser the water, the higher you float. The ball will do the same.

I wasn't wanting to know if a cell was bad, but how fully charged a good battery is.

I was interested in the charge state of a good battery, not if it was f***ed.

Are BMW owners inherently clumsy? I don't seem to have this problem with my car.

I don't even have that, but why would I have spanners floating above the battery, which somehow land precisely across the terminals?

Why would that matter? Were the coveralls electrically conductive?

Then connect the fully charged end last, surely?

I've never had to do that anyway. The spark is created when you connect them up, at which point it's not charging so it's not giving off gases. I just connect red to red and black to black in any order, directly to the battery, why introduce an extra resistance through the chassis, or risk having a lead near moving parts of the engine?

Mine doesn't have any covers, but it's a 21 year old car, they've probably busted by now. There's no reason I would be clumsy enough to drop a spanner accurately over the terminals.

This is a case of changing something because one out of a billion people was unlucky. Health and softy morons need to learn about percentages.

What has the overcharged to do with the spanner? Was it the spanner or the overcharging causing the explosion? And what kind of shit charger keeps on charging after it's full?