how to test battery of a vehicle

[Techgeek121]

My old model car was'nt charging battery enough, first i thought it may be battery issue. but i recently replaced my battery with a new one so there are lesser chances of it. i first check online reasons behind no charging of car batteries and found that it may be due to alternator which may be not charging the battery. So i test alternator of my car, i wana know which is valid method of alternator testing?

 

I found a blog on this  https://www.scienceforums.net/topic/126940-how-to-test-battery-of-a-vehicle/

 

Edited April 1, 2022 by Techgeek121

[swansont]

Your link is to this thread.

[exchemist]

1 hour ago, Techgeek121 said:

My old model car was'nt charging battery enough, first i thought it may be battery issue. but i recently replaced my battery with a new one so there are lesser chances of it. i first check online reasons behind no charging of car batteries and found that it may be due to alternator which may be not charging the battery. So i test alternator of my car, i wana know which is valid method of alternator testing?

 

I found a blog on this  https://www.scienceforums.net/topic/126940-how-to-test-battery-of-a-vehicle/

 

One thing you can try is, when it is dark, get the car to face a wall, turn on the headlights with the engine off and then start the engine and rev it a bit, to 1500rpm or so. You should find the brightness when the engine is off is the same or a bit less than when the engine is running at 1500rpm. If the brightness is less with the engine running than when it is off then your alternator is not charging properly.

But a voltmeter would be best. When the engine is running at 1500rpm the voltage across the battery terminals should be slightly greater than when the engine is off. If it isn't then the alternator is not working properly. (N.B. Do not be tempted to disconnect the battery terminals with the engine running, as the battery smoothes the voltage produced by the alternator. You can bugger up any electronics on the car due to spikes in voltage if you are not careful.) 

[studiot]

1 hour ago, Techgeek121 said:

My old model car was'nt charging battery enough, first i thought it may be battery issue. but i recently replaced my battery with a new one so there are lesser chances of it. i first check online reasons behind no charging of car batteries and found that it may be due to alternator which may be not charging the battery. So i test alternator of my car, i wana know which is valid method of alternator testing?

 

I found a blog on this  https://www.scienceforums.net/topic/126940-how-to-test-battery-of-a-vehicle/

 

 

38 minutes ago, swansont said:

Your link is to this thread.

 

Before you go accusing either the battery or alternator you should check

1) The drive (fan) belt tightness.

2) The condition and tightness of all electrical connections (both the terminals and the cobles) between the battery, vehicle and alternator.
This should include the earth strap.

 

You say you have an older model so it may be OK to disconnect the battery to clean and tighten the terminals.
More modern vehicles can be a pain as you then have to reset all sorts of electrical gubbins.
Garages often keep a spare battery to temporarily connect whilst disconnecting the car abtter for test and maintenance against this problem.

[mistermack]

The above comments give good advice, here's my attempt to give a bit more.

The fan belt should be checked as above, but if you hear an unusual squealing noise coming from the engine, usually when you rev the engine from tickover, then that's an extra clue that it needs attention. 

I use the lights as exchemist advises, but if you look carefully, a good altenator usually brightens the lights when you rev it, and dims slightly when you let the revs drop back down to tickover, so in that case, you can see it's charging, and don't need to turn off the engine.

With a volt meter, (surest method) you will get about 12.5 volts with the engine off, 12.8 with it ticking over, and about 13.3 when revving the engine. (all variable) so if you get a constant 12 to 12.5 when off, and the same or less when running, then it's not charging.

If you find it IS charging, but the battery is flat in the morning, you have a current leak somewhere. A way to test for that, is to charge the battery, then turn every electrical item off, and disconnect the positive terminal at night. If the battery is good in the morning when you reconnect it, it's likely that the battery has been slowly leaking charge overnight. 

A friend of mine found that a usb connection to his dash camera had been doing that, flattening the battery overnight.

[MigL]

To add to Mistermack's excellent advice ...
Lead-acid cells have a potential of 2.1 volts. so six cells in a car battery will give you 12.6 volts ( slightly more, like 12.8 V , due to 'surface charge on a fully charged battery. If your voltmeter reads 10.5 V , one of your cells is shot and you need to replace the battery.
If the engine is running, the alternator will supply about 10% higher voltage to charge the battery, so you should see about 14 C on your voltmeter. If you only see about 12.6 V , you are seeing just battery voltage as the alternator is not supplying any, and you need to replace the alternator ( typical failure mode is shorted diodes ).
 

[Sensei]

I would connect an ammeter between one of the battery electrodes and the cable to see if current is flowing there. If so, it means something is draining the battery overnight.

Energy = Current (from multimeter configured as ammeter i.e. serial, which requires disconnection of battery, and plugging multimeter like above) x Voltage x Time (in Joules). Divide by 3600000 to get it in kWh.

 

Edited April 5, 2022 by Sensei

[studiot]

At the risk of stating the obvious, you cannot fully test a battery with electrical tests alone.

A simple check, not yet mentioned is to check that the liquid in the battery properly covers the plates.
A more complicated one, though still not difficult, is to check the strength of the battery acid by measuring its specific gravity. Garages have a special hydrometer for this.

[mistermack]

It used to be simple to find out if you have a current leak that's draining you battery. Take the +ve terminal off the battery in the dark, and touch it to the terminal. ( with all electrical things turned off ). If you saw a tiny spark, you were losing current. 

Today, that doesn't work, with all the electronics and alarms, you will always get a little spark when you do that, it doesn't mean there is a leak. 

What you can do, is set up your multimeter as an ammeter, and disconnect the positive terminal. Then, with all electical items turned off, touch one probe to the +ve battery terminal, and the other to it's loose connection. If there is a constant current showing, that doesn't drop to zero, then you are losing charge somewhere in the car.

This shows how to set up the multimeter, it's very straightforward : 

https://www.youtube.com/watch?v=P660hTqkGiY

 

[MigL]

Most batteries ( of this century, anyway ) are sealed types, with only a breather.
It is impossible to add distilled water ( unless you're willing to cut a hole and subsequently, silicone it closed ), and may only have a 'cat's eye' to check level.
And most new cars have always on systems ( like clocks, temp gauges, etc ) that draw current even when the engine is off.

A good battery will last 5-7 years. Keep in mind that batteries charge very little, if at all, when engine is idling, and the more often you deep discharge the battery, the more you shorten its life.

[mistermack]

9 hours ago, MigL said:

Most batteries ( of this century, anyway ) are sealed types, with only a breather.

The majority seem to have the gel type electrolyte these days anyway, and topping them up seems to finish them off altogether. ( I tried it ) 

With modern cars, I find that they start so well these days, that you get very little warning that the battery is on its way out. On my old Espace, it would start when the battery was on it's very last gasp. In the old days, a car would need a fair bit of winding over to start, so you could judge how much life your battery had. 

On a petrol car, you can pull out the main HT lead, and turn over the engine with the starter, and you will get a good idea of the life in your battery. But I don't know how to do that on my diesel. It just starts first touch. 

[Techgeek121]

Thanks all for your help.  i found this helpfull also battery test with multimeter.   https://meterreviews.com/how-to-test-a-battery-with-a-multimeter

[studiot]

1 hour ago, Techgeek121 said:

Thanks all for your help.  i found this helpfull also battery test with multimeter.   https://meterreviews.com/how-to-test-a-battery-with-a-multimeter

Thanks for coming back to us to report.   +1

 

You first posted this question in spring, ie at the end of winter.

It is not uncommon for a failing battery to 'recover' during the summer months and fail again the following winter.

So if your tests revealed an elderly and failing battery you have the rest of the summer to get it sorted.