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

Commander Kinsey snipped-for-privacy@nospam.com wrote

Thats not what the green thing indicates.

Not technically possible.

I do believe that little green float is to tell you the physical state battery, not if it is holding a change correctly.

If you want to do a quick check of your battery, dig out your volt meter

1) with your car off, it should say 12 volts or so. if lower, take it to your mechanic. As it could also be your alternator. 2) with your car running, the volts should be about 14.5 volts. If not, something is wrong and it could also be your alternator as well as your battery.

The best test is to take it to your mechanic and ask his to do a deep cycle test on your battery. Their testers will test battery, alternator, diodes, the works. I ask for one every oil change.

And get your oil (and breaks) changed by a real mechanic, not some teenager at jiffy lube.

I don't somehow think its like that. The charged state is hard to work out, as a faulty battery may well seem good, but internal resistance could mean when you want to have a high current, say on a starter, the voltage drops across that resistance, Even modern Lithium rechargeable charge states are only approximate. Brian

Yes indeed, read my last message. All the float tells you is the level of the electrolyte and in some very posh batteries the specific gravity which means how dilute the acid is. Most of the gassing of batteries is water, though you would not know that from the terrible rotten eggs smell!

Brian

The little green float tends to work. The density of the acid must change with charge state. A leisure battery I have sat next to me is green until it drops to about 75%, then it turns black indicating it wants charged. Presumably this float is slowly moving, and could be put in a tube to show the % charge.

I've only once known a battery to have a green float but be useless. It was my car's previous battery, which had been flattened many times. Even after a 2.5 hour drive with a functional alternator, tuning it off for a few minutes it refused to start the car. The AA mechanic said she'd never seen a battery do that.

It is an integral hydrometer. The density of the acid changes according to charge. If the float sinks down and does not rise after charging, the battery is beyond holding a significant charge - even if the terminal voltage has risen (until loaded).

Check with engine stopped and headlights on. A failing battery can stil have the normal voltage off load, but be pulled down when loaded.

I have seen just above 12V unloaded, drop to 8.5V loaded.

This is a DIY group! Doing your own oil and filter change means that you get to choose the brand and quality of oil used. Similarly for brakes.

one that can spell...tee hee

Probably because half the folks wouldn't bother to check it and the other half wouldn't know what it meant if they did.

My wife's five year old Subaru Forester OEM batt went DOA last month. Dealer wanted $240+ to replace. I bought the best lead-acid batt Costco had for just over $100 and installed it myself in 15-20 minutes.

Even though my same-aged Toyota Avalon OEM batt had never hiccuped and tested OK-- while I was at it, I did a preemptive replacement of it too for about the same price and install time.

I don't think you mean DOA, that's Dead On Arrival, in which case you would have got it replaced under warranty.

WTF? Even the cowboys round here don't try to charge that much for batteries. Although I was just asked to pay £180 + fitting for a catalytic convertor I didn't need. I asked if they could weld it, after pointing out the MOT failure was about an exhaust LEAK, not an emission failure, and he said he didn't have a welder (WTF?). I took the car to a welder and he said there was nothing wrong with the cat, the leak was from the neighbouring part! He then found the correct part on Ebay for me to buy.

Maybe he was trying to sell you an AGM battery. Unless you're in the habit of running it flat many ties, not worth it.

All batteries are the same. It's not like Li Ion where the Chinese rip you off. A crap Lead Acid with less lead would be obvious when you picked it up and felt like superman.

I paid about £40 ($50) for a 60Ah battery. I paid about £75 ($85) for a 130Ah battery. Was yours more than 130Ah?

What a waste of money. If you're that fussy, you could have just tested it.

Most car batteries are sealed now, not refillable, and don't have a float indicator. Mine is under the trunk in the back and is not even visible.

Brian Gaff snipped-for-privacy@gmail.com wrote

Something very fucked somewhere if you are getting a rotten eggs smell.

Exactly.

My car has an AGM (absorbed glass mat) battery. At 5 years replaced it. Planned a long trip, not every store carries H-9 size and since it is 66 pounds I let Advance Auto do the swap. Also, not every place will do a free swap if it is in the trunk and they did. Worth what I tipped him.

It's often the sealed ones that have the hydrometer - as you can't open them to sample the acid with a handheld one.

Why can't we just watch it with a volt meter? The open and load volts are all we need.

A Bluetooth OBDII scanner and the Torque app for your phone will let you monitor that and much more on modern vehicles

That is a great test. Removed the alternator from the equation.

Chuckle! Turn your emergency flashers on and watch your volt meter needle wiggle!

I use to change my own oil, but got to old for it.

It takes a bit of wisdom to know when to do things yourself and when to hire a professional!

About 40 years ago, I use to get my breaks done a Midas or some where similar with a life time guarantee on the pads. Nothing but problems. They saw me every year for new pads, etc..

Then I used a real mechanic from my brakes and needed them changed every seven years or so. And no leaking lines and faulty this or that and no having to drive to Midas on my emergency brakes with brake fluid spraying all over the road. That was a trip!

He who pays the least, pays the most! Learned the hard way.

Then, the answer to the OP question, is use a proper hydrometer (no balls, but a graduated floater).

I have mine somewhere, but batteries nowdays are sealed.

Right. That's a good and quick test.

Well, for me this is an electronics design group :-)

You need a proper hydrometer, and use it on each of the six battery cells.

The integrated one, with balls, only measures, and roughly, one cell.