Battery testing

MikeT · Unread post by **MikeT** » 25 Oct 2008, 12:53

Is there a DIY method to determine a battery's condition without resorting to fitting it in the car and cranking the engine?

citronut · Unread post by **citronut** » 25 Oct 2008, 15:28

if you have a resonably good battery charger, stick it on at its highest charge rate, after removeing the caps/lid from the top of the battery, observe the fluid, if any sell is bubbleing very fast compaired to the others, you have one cell cream crackerd, or buy a cheap hydrometer

regards malcolm

Clogzz · Unread post by **Clogzz** » 25 Oct 2008, 15:46

The voltage should be 12.5 Volts minimum when cold and without load.
There are proper battery testers with a voltmeter and load resistor.

The water levels are a good indication.
When the battery is on the way out, the levels on the positive side are dropping.
Normal level is the top of the plates just under water, hoping it hasn’t just been filled from the tap, or from the gutter.

If all levels are low, the battery is cactus.

Where we are, it’s impossible to find batteries that last much more than two years.

The original Japanese batteries used to last six years.

MikeT · Unread post by **MikeT** » 25 Oct 2008, 18:10

My battery charger has died of old age

Would it be ok to use a 12v torch charger? It's rated at 12V 0.5Amps max so I understand it could take a few days to recharge a flat diesel battery. My Xantia battery is sealed for life and has a flame arrestor vent so I can't see the electrolyte level or test it with a hydrometer.

I would like to mimic a load tester if possible. Can I use, say 55W bulbs or a spare glow plug? I'm unsure how to calculate the load and time needed for a good battery.

Unread post by **myglaren** » 25 Oct 2008, 19:55

You can do a quick and dirty load test by turning on the headlights with the engine off.

If they dim appreciably after a couple of minutes the battery is a goner, assuming that when the engine is running the voltmeter shows 12V.

Most motor factors will do a load test for you though - only go to one you trust as some will sell you a new battery even if the old one is OK.

48 hours on a trickle charger could do it the world of good though, if it is in a slightly discharged state and the alternator isn't able to make it up (to many short trips, no long ones).

citronut · Unread post by **citronut** » 25 Oct 2008, 20:30

a battery can show 12V on a volt meter but still not have enough to cranck an engine over, and with engine running and revs at about 2,500 RPM you should see around 14 to 14.5 volts on a volt meter,

also it will take a very long time to charge it up at 0.5amps

regards malcolm

MikeT · Unread post by **MikeT** » 25 Oct 2008, 20:49

Apart from the engine being a non-runner right now, the battery is not fitted either, it's in my flat. It's been "trickle-charged" for more than 24 hours and stood a further 48 hours and currently reads 12.95V (was over 13V immediately after charging).

reblack68 · Unread post by **reblack68** » 25 Oct 2008, 21:12

I would leave it off charge for a few days then persuade somebody to let you try it in their car. To really see what it's made of try and start a diesel from cold.

I don't think there's any easy, or safe, way to simulate a cold start.

MikeT · Unread post by **MikeT** » 25 Oct 2008, 21:28

I'll have the ideal test car for it soon - mine. I'll be cranking without starting to prime the fuel and oil before I think about starting it. But I'd rather not have it fail on me at that stage, hence the need to test it first.

citronut · Unread post by **citronut** » 26 Oct 2008, 08:40

if its showing 12.95V i would say it if good, just go for it Mike

regards malcolm

Unread post by **Old-Guy** » 26 Oct 2008, 14:42

Wearing a different hat, some 20 years ago I developed and manufactured a solid-state Battery State Indicator called 'VoltWatch'. As a result I learnt quite a bit about lead/acid batteries. It's a complex subject, but I hope the following helps rather than confuses:-

An indicated battery voltage of 12.95V after 48 hours 'resting' proves 2 things:

1. All 10 cells are live,
2. and will hold a charge.

Unfortunately, it gives no idea how much charge (in terms of AHrs) the battery will take or if it can actually deliver an adequate cranking current. Generally, a battery that will take and hold at least 50% of its rated capacity will happily crank an engine it's intended for.

For a thorough explanation of the relationship between indicated battery voltage and % state of charge of a battery http://www.attfield.dircon.co.uk/page20.html

For a DIY test method for battery capacity, http://www.attfield.dircon.co.uk/info-indx.html#Testing

A word of caution: only expensive, test calibrated, Digital Voltmeters are accurate to better than about 0.05V and individual battery manufacturers tweak the chemistry inside their batteries (the lead alloys used in the plates) so what you see on a DVM may differ somewhat from those quoted in the web pages above.

Guy

Unread post by **Old-Guy** » 26 Oct 2008, 14:50

Clara.net have managed to corrupt the text on my pages and screwed up customers' FTP passwords so I can't upload clean pages. As soon as I can get into my webspace, I'll sort the problem.

In the meantime Mike, if you need a readable copy of the test method, e-mail me and I'll send you a PDF file.

MikeT · Unread post by **MikeT** » 26 Oct 2008, 17:01

I've linked to the test page and it looks good so off for a read now. Thanks. By the way, not sure if it complicates matters as you mentioned chemistry nobbling but the xantia battery (the one that read 12.95V currently showing 12.92v today) is not lead but calcium, which the manufacturers claim can handle a faster more powerful charge and depletes less readily.

Unread post by **Old-Guy** » 26 Oct 2008, 17:53

Mike

'Calcium' is short-hand for 'calcium alloy' meaning the lead is doped with a very small proportion of calcium that improves both its electro-chemical and physical properties. Most batteries use this technology even if the manufacturers don't say so - even those made from recycling batteries (a proportion of which will inevitably have been calcium).

At heart, it's still a 'lead/acid' battery with voltages perhaps 0.05V higher - not enough to make any practical difference even if your meter were accurate enough to detect it.

Best of luck

Guy

MikeT · Unread post by **MikeT** » 27 Oct 2008, 11:15

Hi Guy, clever marketing BS then

It's one of these http://www.batterypower2000.co.za/downl ... ochure.pdf

The battery's reading 12.89V this morning though it was only "trickle charged" anyway. Is 60Ah powerful enough, I can't see the specification in the Haynes manual?

I've also "rescued" a discarded 72A battery that had almost dry cells. After topping up with pure water I was suprised to see it take a charge so ran a 55W bulb off it which lasted four hours without dimming noticeably. Between the two I should have enough power to prime and start the xantia when needed.

I did think of testing/charging them in my Granada but that car starts so easily, I reckon a PP9 could do it

I guess I'll have to bite the bullet and buy a smart charger.