Cheap 12 volt battery testers. Are they any good?

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NPMR

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Batteries on the boat ( 5 of them) are between 4 and 6 years old. Could drag them out of the boat to a battery retailer who'll test them for free. Or get an electrician in, who'll do it for about the same cost as a low cost 12 volt Cold Cranking tester/analyser. Which I would then own to use and lend in the future, given that the batteries can only get older.

Why wouldn't I buy one?
 
NPMR said:
Batteries on the boat ( 5 of them) are between 4 and 6 years old. Could drag them out of the boat to a battery retailer who'll test them for free. Or get an electrician in, who'll do it for about the same cost as a low cost 12 volt Cold Cranking tester/analyser. Which I would then own to use and lend in the future, given that the batteries can only get older.

Why wouldn't I buy one?
Click to expand...

Buy one but buy something worthwhile

Fluke make a good one http://uk.farnell.com/fluke/fluke-b...ead-acid-li-ion/dp/2445944?st=battery testers
 
Those cheap testers do have their uses. Mainly for starter batteries. Or when you want to rule out a starter motor as being the problem.
But for house batteries, start current doesn't tell you ever so much.
I've seen old batteries with very seriouly reduced capacity, like down to 10%, that will still put out a good start current for 20 seconds.
For a house battery, a more useful test is generally moderate discharge for half an hour or more and see how the volts hold up.
 
NPMR said:
Batteries on the boat ( 5 of them) are between 4 and 6 years old. Could drag them out of the boat to a battery retailer who'll test them for free. Or get an electrician in, who'll do it for about the same cost as a low cost 12 volt Cold Cranking tester/analyser. Which I would then own to use and lend in the future, given that the batteries can only get older.
Why wouldn't I buy one?
Click to expand...

This may seem daft and to practical.... but why not turn on the lights etc that you require power for, do a quick calculation of the power being used, watch until things begin to fade and from that extrapolate the life remaining in the batteries..

There are many theories about batteries and their reliability but my experience is that it comes down to manufacturer's quality more than price, I just moved a digger that has a battery in it which was not charged for at least a year but it was a good battery, about 3 years old, always was a good battery and was the replacement for the original caterpillar battery that was in the digger since 2001,

moved a jeep that had a new battery a few months ago and it was flat, (this had been disconnected) this was a cheaper battery from a local source... similar experience repeated several times over.

My boat has 3 agms I put in in 2006. they were left unused for 5 years from 2008 to 2013, and were utterly flat, charged with an old caravan charger and a desulphator for a few weeks and all three were absolutely fine for the next two years with the boat on a swing mooring, in the Yard for 2 1/2 years since with the last few months on a new hi tec...tricle charger and they turn the engine over and run lights etc as if new ( I often leave lights etc on for a few days to run them down and then charge up again)... I intend to disconnect charger over the weekend and if the batteries will start engine at end of March I will consider them to be fine for this coming year, ( once I launch I will probably carry a spare starter battery and jump leads with me just in case)

All of this is of course blasphemy to some

Just for good balance I also have a 1-2-both switch( I refused to have VSRs I had them in a previous boat) and I have a split charge diode.

Experience often shows that things may be fine in practice which are impossible in theory....
 
pandos said:
Just for good balance I also have a 1-2-both switch( I refused to have VSRs I had them in a previous boat) and I have a split charge diode.
Click to expand...

I don't want to make this another 1-2-B thread, you're perfectly entitled to fit whatever you want, but that's a bit of an odd statement.

If you're reason for fitting the 1-2-B really was because you didn't want a VSR, there was no reason you couldn't have fitted separate switches with the diode. Although, you will be getting an unhealthy voltage drop through the diode.

Experience often shows that things may be fine in practice which are impossible in theory....
Click to expand...

That's very true. Real World experience trumps googled snippets any day, IMO. :encouragement:
 
Battery testing is fraught with problems. Not least of all that a battery can drop dead of internal fault without warning degradation.
As said a battery has to achieve 2 functions. One is to provide a high current for engine starting hopefully for a decent amount of cranking. (in case of engine problem) and secondly to provide a low current for a long period.
To make a tester for these you have to dissipate huge amounts of power (heat) while observing voltage. Then you have to be able to waste a low power for a long time. (while monitoring voltage). Neither of these suit the concept of a simple tester. Some people reckon they can produce algorithms to predict battery worth with a small amount of testing but I doubt it's use. Essentially we have multiple batteries in a boat which can be isolated and which will provide redundancy when one or more drop dead. It is usually obvious when this happens but if not then comparison with performance of other batteries with isolation will show a problem.
So you have 2 testers on your boat. Your engine starter and your normal domestic load. Just use them judiciously to estimate worth of batteries. olewill
 
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