Battery analysers

[zoidberg]

There's a lot of those things available via Temu, etc. for around £15-20 or so.

Are they really any use? How otherwise can I determine the 'state of charge' or ability of several AGM batteries to earn their keep?

 

[fredrussell]

Thread 'AI Generated Content'

15 Oct 2025

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[oldgit]

I usually borrow a very expensive professional piece of kit made by "Snap On." with a printer.
Its owners frequently use it in arguments about battery condition, normally in "Your battery is knackered and you really need to buy a new one" debates.
After work has been carried out the customer returns with "You have done somehing to my car, the dash is now displaying warning lights galore"
Certain vehicles were notorious for this, a new battery always solved the problem.
Unfortunately customers did compound problem by buying some cheap and nasty battery with less capacity.

Device cost well over £1 K and would still give different verdicts on the same battery with multiple tests.
Normally went with best of three.

 

[Refueler]

I still like the older bridge tester that most breakers yards and garages had ... two handles on a large plate frame - inside the frame a huge resiatnace and then a meter to display battery maintained voltage when applied.

 

[PaulRainbow]

I still like the older bridge tester that most breakers yards and garages had ... two handles on a large plate frame - inside the frame a huge resiatnace and then a meter to display battery maintained voltage when applied.

Still good for testing a starter battery, but for domestics you can't beat applying a known load for a given time to test real World usable capacity under realistic loads.

 

[Neeves]

I' not convinced that buying a battery testing device is a good investment, how often do batteries fail (in the UK), actually they don't fail- they just get old. You buy a cheap battery performance device - you probably use it because there are signs your battery is not performing (but you knew that anyway - that's why you tested the battery). Why not go to your nearest battery retailer and ask him to test your battery - that's why they have the kit (their kit is not there to prove their batteries are good - but to prove your battery is bad.

If the starter motor grunts on a cold morning then the battery is probably at fault. Use that Lithium jump start you bought for just such occasions, start engine and go to the nearest battery retailer. This latter will be more than happy to prove your battery has seen its best days. Ask him how much his test kit costs, to validate the price quoted in post 4. Think yourself clever to have bought a cheap Lithium jump start device. *Coincidetally Lithium jump starter )

Specifically take your AGMs to your battery retailer - he will be happy to test them - its good PR - even if you don't buy then - you will recall he did the check for free. Why would you go to anyone else - unless his prices are daft (but its a competitive market, its not got 'marine' in the name )

But just out of interest why are you collecting old AGM batteries - when new they are not cheap and unless you keep the, charged, basically - look after them - then they are probably duds. Odd devices to collect.

Jonathan

 

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[noelex]

Still good for testing a starter battery, but for domestics you can't beat applying a known load for a given time to test real World usable capacity under realistic loads.

As Paul has indicated, a capacity test is the gold standard for house batteries. Nigel Calder recommends doing a capacity test on your domestic batteries once a year; personally, I think this is excessive. The test is reasonably involved and hard on batteries (particularly lead). But it is certainly worth doing a capacity test if you suspect there is a problem.

A capacity test can be done with adequate accuracy without any fancy equipment, just some effort and time (Google will explain how it is done). Alternatively, there are now relatively inexpensive devices that make the process easier and more accurate.

 

[thinwater]

Still good for testing a starter battery, but for domestics you can't beat applying a known load for a given time to test real World usable capacity under realistic loads.

And applying temperature correction to voltage. Where I sail the bilge can range from 90F to 30F, which can make a 90% winter battery seem like an 40% summer battery.

 

[Refueler]

Still good for testing a starter battery, but for domestics you can't beat applying a known load for a given time to test real World usable capacity under realistic loads.

Yes agreed as then you are testing for two different parameters ...

The old two handled tester - gives you results of whether battery can deliver the power to start a car ...

The known load at a much lower rate gives results as you say if battery still has capacity.

Its not unknown for a battery that cannot start a car - to still be able to deliver lower power demand for significant period as a domestic source.

 

[Big John]

You can not go wrong with the TOPDON BT100. Quick and simple to use and a direct digital readout following the test. https://www.amazon.co.uk/TOPDON-100-2000-Automotive-Alternator-Motorcycle/dp/B08GPD1QV5?th=1. Check out the video's.

 

[noelex]

Yes agreed as then you are testing for two different parameters ...

The old two handled tester - gives you results of whether battery can deliver the power to start a car ...

The known load at a much lower rate gives results as you say if battery still has capacity.

Its not unknown for a battery that cannot start a car - to still be able to deliver lower power demand for significant period as a domestic source.

This is a good point. For a start battery, the short-term delivery of a high current is needed, and this is best tested with a traditional car battery "tester". For a house battery, we need to know the amount of energy that can be extracted. This is best measured with a capacity test.

If a battery has "gone to God" it will commonly fail both tests,but as cranking amps are limited for true deep cycle batteries, these batteries can sometimes record a false positive "fail" result on a car battery tester unless the device is sophisticated and set accurately.

Doing a definitive capacity test on any deep-cycle battery you are considering scrapping is often worthwhile.

 

[Refueler]

True Deep Cycle batterys ... not the so-called Deep Cycle often sold out of Chandlers etc - are not designed to crank engines .. it buckles the softer plates.
The 'Deep Cycle' batterys often sold out of such - are compromise batterys - what I would call semi-deep cycle !

 

[noelex]

True Deep Cycle batterys ... not the so-called Deep Cycle often sold out of Chandlers etc - are not designed to crank engines .. it buckles the softer plates.
The 'Deep Cycle' batterys often sold out of such - are compromise batterys - what I would call semi-deep cycle !

True. Sometimes real deep cycle batteries cannot generate sufficient cranking amps or the required internal resistance to satisfy the expected requirements of an automotive battery tester.

A capacity test is the better alternative to determine the health of this type of battery.