battery hydrometer

It all depends on how often you're going to use it. If it's for use in a garage, go for the Sealey. If it's going to be just now and again for personal use, just get one of the floating disc/ball jobbies.

since most batteries are now maintenance free it is not likely to get used a lot, unless you have a specialist application.

The calibrated ones (that actually read specific gravity are the best, but a two quid floating ball type is almost as good. I used to use one for testing motorcycle battery cells and it always seemed to give a correct result. I really cannot remember the last time I used one at all though.

A accurate DVM is actually more use in general terms, and a loading type tester is even better.

Please don't get me started on that again ;)

I posted about battery testers a couple of weeks ago and I was told that testing under load with a DVM was the way to go. Apparently the people round here didn't like the load testers because the load of the tester doesn't necessarily equal the load of your starter motor. I had read quite a few old posts recommending load testers and was about to buy one until everyone here talked me out of it!

real world testing is good: starter load and see what the volts drop to, but....

I use a load tester on every service to check the battery condition, but it doubles as a very useful diagnostic for bad battery connections, engine earths etc. Mine was from snap on and cost about 150 quid 20 years ago or so.

I don't think a load tester 'has' to equal the load of a particular starter motor, to give give a good idea of a batterys cranking capability. They do put a heavy load on a battery, and as long as the volts don't drop during the test, the chances are that even a higher load wont make a significant difference. Mike.

Yep, it does, battery resistance is very non linear. If the volts don;t drop during the test then your tester's knackered :-)

Of course there is an initial drop when the tester is switched on after it reads the no-load volts, but the voltage shouldn't drop during the 10 secs or so when the test load is actually applied.

If it does drop with a fully charged battery, IME the battery is no longer reliable. It might still start the car in the summer, but come winter and cold mornings and the chances are that it will not.

I've had my load tester for well over 10 years. I know how to read it and I also know it's not knackered. Mike..

If the battery volts do not decrease to some extent when the starter operates or the load is applied then you have the tester connected to the wrong battery. It is a fundamental principle that the battery volts will go down when load is applied, the extent of the drop can give some indication of the battery condition/state of charge, with knowledge of the ambient temperature and the size of the load you can judge battery condition.

I think you are misreading my post. My load tester has a spring loaded switch to apply the load. When first connected it simply reads the no-load battery voltage. When the switch is depressed to apply the load, the voltage reading drops. If the voltage continues to drop, assuming the battery is fully charged, the battery is on it's way out, and should be replaced. A constant voltage reading during the time, (10 secs or so) the load is applied would indicate the battery is OK. Mike.

At that load. Which was the point the rest of us where making, if you don't know enough to work the answer out from the dvm during starting then a battery tester doesn't give you a pass/fail result, if you do know enough then they're a usefull source of information, but again you still have to interpret the difference between a Ford Ka's battery & a diesel Landrovers.

Which was why I wrote 'would indicate'.

My point was was that IME, any drop after the load is applied with my tester, would indicate a failing battery. Obviously a higher load wont alter that situation.

Which in effect is simply doing a load test.

Within reason, whatever a cars batteries capacity is or it's cold cranking amps, if it fails a test with my load tester, when it's charged and not low on electrolyte, it's on it's way out. That doesn't mean if it passes, there is nothing wrong with it. Which it would appear, is what you think I'm saying. Mike..

No, I think we're agreed on that, the problem is that a faulty battery can pass, without knowing the load your tester applies & the load the vehicle applies then it doesn;t tell you much.

Particularly if it is a remote mounted large battery on a diesel (this one fooled me for a while), in the end I changed the battery on spec. and the problems disappeared, but standard load testers showed no fault, while a DVM showed it dropped to about 6 volts when cranking) It was a diesel CF Bedford by the way.

You seem intent on emphasising the negatives of using a load tester, rather than it's positives. The tester I have is designed for car batteries, not very heavy duty batteries, but the fact remains that unless there is something obviously wrong, like low electrolyte etc,.that if any size battery fails a test with my load tester, further tests are very unlikely to show the battery is any good.

I'm not saying that a load tester is a foolproof way of checking batteries, just that a fail result, even with a low load current tester is a positive. The battery might as well be scrapped. OTOH, I know a pass doesn't mean a battery is in good condition for a particular application.

The battery on my car, a 528i BMW, is a heavy duty one. 95Ah, CCA 850. I imagine it could deteriorate quite a bit before it showed a fail on my load tester. Mike.

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The point being made is that unless you can already work out the answer then it still doesn't tell you anything. It's quicker & more convenient but the answer isn't good/bad . & you can get at least as much & nearly always more information by just cranking the engine with a meter across the battery.

That's OK if you only have one car and it's at home, but for many years I have as many as five. ATM I have four. Three in lockups locally and one I'm using. Their batteries are in my w/shop, regularly charged. Whilst a voltmeter, and a hydrometer are useful, they don't tell you if a battery is still capable of starting a car. My load tester does.

To you it would appear that a load tester is not worth having. To me it is. It can save me a trip to a lockup with a battery, only to find when I get there that it wont start the car. Mike.

Out of interest, how can you find out the CCA of a particular car?

Stephen gurgled happily, sounding much like they were saying:

If you mean "of a particular battery", look at the label on it. If you mean "the battery requirement of a particular car", look at the handbook.