Car battery oops

Complete bollocks.

Lead antimony is between 8 & 40% per month, car batterys tend towards the higher end of the range.

I have a spare battery kept indoors which doubles as a supply for an inverter to run the central heating in event of a power cut. I've just checked it with my tester and it's reading 59 amp/hr on a nominal capacity of 70 amp/hr. Which makes it 15% down - assuming it is the full 70 when fully charged, which I can't remember. And it's way over a month since it was charged.

60% a month rivals the worst other types of rechargeables. Lead acid is among the best.

Checked it again this morning and after sitting for 4 days it's still showing 12.84v. The voltage has actually gone up again. My gast is well and truly flabbered. It appears to have been completely rejuvenated but I doubt that's possible. Can surface charge still be present after so long and after having put a small load across it for a while last week? Can it still really be in good condition after 8 1/2 years use in less than ideal conditions?

I guess I now have to keep the car for another 8 years to find out how long the bloody battery will last. I fear the car might die before the battery does.

In message , Duncan Wood writes

I modified a mainframe computer PSU to use as a general PSU/battery charger, which has a crowbar shut-off if the current exceeds a preset value. It cost me about a fiver for the original at a surplus outlet. I don't know why they don't use a similar system in commercial chargers. Too expensive?

It's the leads being unfused that I object to, whether or not the chargers attached.

Must be psychic. On sale next Monday. But gone up to 14.99. Still good value though - others charge more than double for the same thing.

In message , Duncan Wood writes

I should have read more closely. :)

You've personally tested it with a series of batteries yourself then have you? In controlled lab conditions? I have and the results are unarguable - a lead/antimony wet cell battery with pasted plates at 25C will lose 58% of it's charge in the first month as evidence both by gravimetric testing and controlled discharge testing.

Did you doa gravimetric test of the electrolyte? Have you discharged it to fixed endpoint voltage into a standard load? Unless you have you cannot easily say what it's charge state is - open circuit voltage is not good enough

No. *Some* lead acids are amongst the best. Many of them are amongst the worst.

Yes. The original Focus were supplied with standard Motorcraft wet cells (not silvers until about 2003 IIRC) and they last amazingly well if the batterys are not stressed by constant stop/start working. Mine has gone

9 years now and just been replaced as I was going into the Alps and didn;t fancy a problem. A freind has one that has ten years of service and again seems to be perfectly fine.

Both were tested a while back and were considerably down of capacity (38Ah and 32Ah compared to a design spec of 65Ah) but still were excellent on voltage and CCA. Terminal voltages are a poor indicator of capacity.

I've just told you about one which didn't. And it would surprise me to find a fully charged battery flat in such a short time - unless faulty.

No - I used a modern electronic tester. But it only told me something I already knew.

40% isn't unusual, you'd normally never notice on a car battery as the CCA won't drop much at that point & that's all you normally care about.

But I do care since it's possibly needed for running an inverter. Where actual capacity does matter.

Well if you're intending to leave it for a month 1st then a high antimony batterys going to be a sub optimal choice. But if you're intending to use it for that you'd hardly buy a car starting battery.

It's actually a spare for the old car. And having installed the inverter and changeover switching some years ago it's never been needed. If it were used a lot I'd get a leisure battery just for it.

But so saying I've used car batteries for running pro sound gear. Provided you don't run them very low they can be a more cost effictive option then specialised ones. I had two which were alternated - one day each - on one job and used 5/6 days a week for over two years. They cost under 40 quid each from Halfords.

If you don't run them very low then you can just use a smaller deep cycle, if you're going to use it as a car battery as well then it's cheaper.

I was under the impression that deep cycle batteries required relatively (to a car requirements) lower output current and lower charging rates?