battery testers

I assume it shows the amperage being drawn. Depending on the drop off rate combined with seeing if any of the cells are bubbling, you'd get a better idea of a batteries condition than measuring the voltage alone.

Assuming the battery is in the car you have a ready made high load in the form of the starter. Measure the voltage when this is operating - a peak hold DVM makes this easier.

There are very sophisticated electronic testers that can determine the condition of a battery - but these are pretty expensive. Most decent battery shops will have one and will test for free.

If you Google you'll find plenty of information on testing your battery and charging system using an ordinary DVM.

Sorry if I have misunderstood but don't you want to know the lowest voltage it drops to when starting the motor rather than the highest?

Do you need to disable the engine in someway so that the starter motor turns but does not start anything? I presume if the engine fires up you are effectively testing the alternator not the battery?

Thanks.

Indeed. Sorry to not make it clear - peak hold types usually give you the choice of max, min or average. So I called it the wrong thing. Perhaps data hold or memory is better.

As I said one with a memory function can let you read the minimum voltage. Ebay will have a big selection starting from perhaps 25 quid new. Or of course places like Maplin. I'm not over impressed with Gunson stuff value wise.

Thanks for explaining. If it's the lowest voltage then it would be ok to have the engine fire into life. I've not had a multimeter with memory before, so this was new to me. I just found the Gunson site by google. Are the items good quality just badly priced or are they poor quality and badly priced?

Thanks again.

It's a bit difficult to say since they often offer features which make them unique. The only thing of theirs I've ever actually bought is their CO meter which also does RPM and dwell. The CO meter is pretty inaccurate

- which is I suppose understandable since a good one costs a great deal, but the dwell and rpm are inaccurate too.

As regards what is good value for a memory DVM, I'm not sure. They tend to change design regularly. And brand names. I have a Fluke which cost more than most DIYers would wish to pay. Its predecessor - which still works fine - is a Maplin own brand. They certainly have a big selection, and hopefully you'd get what you paid for there, value wise.

By far, the best tool to determine battery quality is the multimeter. In fact, a voltmeter on the dashboard reports far more useful information than an amp meter.

The meter reports battery quality AND charging system. The battery test does not provide sufficient load to report sufficient information.

First, battery voltage must exceed 12 VDC when battery has been sitting without load or charging. Next, turn on high beams or other load. Battery should still remain about 12 volts. 11.5 volts suggests either a defective or failing battery; or a seriously discharged battery.

Third, start the engine. That voltage must be above 13 volts. With engine running, add loads such as rear windows defogger, high beams, and heater fan. That voltage must still remain above 13 volts. Now the meter has tested the charging system.

Most important, a multimeter provided numbers. Those numbers tell you what the battery tester would have reported; and more. And those numbers mean others with greater knowledge may provide further information. That is multiple reasons why a tester reports little that is useful.

Meanwhile, the meter also has other useful purposes. The battery test has no other useful function. This is a hands down - no doubt about it - answer. The test is inferior in every way compared to the multimeter. Even its 'loading' abilities are inferior.

The test has only one purpose. It does not scare people who always fear numbers. Nothing more.

WEll barely adequate quality & very overpriced compared with a brief search on Ebay.

Fluke are indeed both excellent and pricey- I have both a Fluke DVM and IT test kit at work and they are reliable, accurate, and durable, but I'm too tight to buy Fluke gear myself. To be honest, even a real cheapy from maplin will do quite well, provided it has the features you need.

Sorry, I'm a bit confused. Are all Gunson products terrible or are we just talking about their multimeters or their battery testers?

Some replies were talking about multimeters giving numbers. I agree that one of the products I found - the Gunson start test just has LEDs which do not tell as much, however the battery load tester seems to have had its analogue dial replaced with an LED voltage readout, which would be as good as a multimeter, wouldn't it?

The battery load tester looks identical to other battery load meters made by Draper etc. Are your criticisms of these testers valid for all makes or is the Gunson particlularly bad? Why is their load insufficient? Do you mean that the load is not as heavy as a starter motor? I agree that whereas this tool is only useful for battery tests a multimeter would do many other jobs.

I had heard of fluke and I do have a Maplin meter, only it doesn't have a memory function.

What were you searching for on ebay? It was on ebay that I saw these various Gunson items, much cheaper than the RRP in shops.

Thanks.

If you mean this

The Draper ones are pretty tat as well, yes. You seem to pay an awfull lot for marketing & a badly calibrated frequency meter to stop you having to divide by the number of cylinders over 2.

Generally yes. And you normally can't adjust it. Sticking a cheap multimeter with a min max reading on the starter terminals tells you more for less money.

To provide a useful load, the tester would become too hot to hold. Obviously, high beams provide a more informative load. And the load to also test the charging system - well, to be sufficient, the Gunson would burst into flame.

Numbers mean at least three digits. A 3.5 digit multimeter that costs about same provide must better resolution AND has numerous other functions. Little in that Gunson product appears useful other than it can probably survive mashing in a box with wrenches and hammers.

Oh no, I wasn't going to spend that much!

I was looking at:

There were several posts saying that testing the battery voltage with a multimeter was useless. I have since read more posts and see that there seems to have been great disagreement over the use of multimeters with just as many people for them as against them. I don't suggest we start that flame war again! MM supporters said that the people who don't like them are not using them properly. I wonder whether people using mulitmeters incorrectly were not testing under load? Perhaps they had simple real-time meters, like me, so could not test the voltage drop on starting?

Even so, isn't there some value in testing the battery voltage "at rest"?

I am confused because the description on that web page says this tester tests up to 100Amps. Is 100A too little? It sounds like a lot to me. OTOH I guess jump leads are rated for several hundred Amps. Won't a battery fault show when drawing 100 A? Why would you need to adjust the load on the meter: to match the exact load of your engine?

I will buy a max-min MM but just trying to understand this other type of meter.

Thanks.

Well it does look well ventilated! Surely it just tests for a fraction of a second?

How much current to high beams take? Surely not 100A?

I agree that for the forty pound mark the MM is a better value for money buy because it can test lots of things but this Gunson tool can only test batteries for the same money.

It's a 0.13Ohm resistor, so it will pull upto 100A out of a charged battery, but your car may pull more or less than that (e.g. it'll be utterly useless for testing a NA diesel Landrover, that pulls about 850A) so in general waht you want to know is what voltage your car battery drops to when your car trys to start. Plus you need to know the state of charge of the battery or you may just have demonstrated that it's a bit flat.

isn't bad for following what's an issue. Testing voltage at rest is where the flame wars come from, it's essentially meaningless.

Not if you actually want to know anything. The Gunson does beat the headlamps though & it won't catch fire.

=55W*2/12v = 9.1A. Which is enough to tell you if the battery's charged, but not anything about it's ability to deliver starting current.

Why are you spending so much money on a multimeter that does everything and more than then Gunson tool can do. 3.5 digit multimeters routinely sell for less than 20 pounds. But then you need not even spend that much. You said you already have a multimeter. Why spend wastefully on a Gunson tool that can only accomplish less and that costs more than 20 pounds?

Whilst agreeing in principle, some Gunson DVMs also do RPM and dwell. This might make it worth the extra money. Although dwell was originally for points it's also quite useful for other fault finding - it can show injector duty cycle for example.

Although most £20 multimeters do that now :-)