Checking battery level

[garry63]

Hi all
If you don't trust the onboard control panel readings for the state of your batteries, then whats the best and most accurate way of telling how much is left in your battery?

 

[Two on Tour]

You can only really get a true indication of your battery state of charge either by using a multi-meter directly across your battery terminals or a shunt with all of the negatives of your circuits going through it.

 

[garry63]

You can only really get a true indication of your battery state of charge either by using a multi-meter directly across your battery terminals or a shunt with all of the negatives of your circuits going through it.

If you use a multimeter can you do it with everything still connected to the battery or do you have to remove?

 

[VXman]

I have always used a multi meter. I generally reads 0.2 volts higher than the control panel (Burstner). Now I have a Victron MTTP controller with Bluetooth my phone can tell me!

 

[VXman]

If you use a multimeter can you do it with everything still connected to the battery or do you have to remove?

If you measure it when it is charging (i.e you have a solar panel or the engine running) then it will show the charging voltage (higher) so not a true reading of the battery state. Same if something is using power at the time. (lower reading)

If there is no charge coming in and you are not using anything (and this has been the case for an hour or 2 so that the battery has 'settled') then yes you can read it in situ.

 

[Guigsy]

With a lead acid type battery, you can tell the approximate level of charge from the battery voltage when there's no load. High loads will temporarily drag the voltage down. Charging will just tell you that voltage of the charger. (Note that with lithium, voltage isn't a useful indicator of charge because the voltage is almost the same throughout it's charge range.)

A more accurate measure is to use a shunt. This adds up all the current used over time, so it can see your amp-hours left. A well setup shunt can tell you battery status even when charging or under load. It'll also give you an idea of how much current is going in or out of the battery right now.

 

[Stealaway]

Hi all
If you don't trust the onboard control panel readings for the state of your batteries, then whats the best and most accurate way of telling how much is left in your battery?

The only way to check battery charge condition is with a voltage meter.
As above take an accurate reading with a multimeter off charge ideally and check your voltage meter readings. If you remember the discrepancy it will become a good gauge to refer to.

 

[Two on Tour]

The only way to check battery charge condition is with a voltage meter.
As above take an accurate reading with a multimeter off charge and check your voltage meter readings. If you remember the discrepancy it will become a good gauge to refer to.

Rubbish, a shunt will give you the state for charge whether the battery be in a state of charging or discharging at any time were as multi-meter will only give you a semi accurate reading when the battery is at rest.

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[Spriddler]

whats the best and most accurate way of telling how much is left in your battery?

A test meter will only register the battery's voltage. A battery can show a good no-load voltage on test but be more or less knackered. A discharge test is necessary to determine the health/available capacity of a battery.

 

[Langtoftlad]

I've got one of these...

Good enough as a double check of the control panel readout.

 

[Pausim]

I agree with Spriddler voltage is a very poor indicator of battery condition. In a 90% sulphated battery the 10% that is still working normally may still hold a good voltage.

 

[headlight]

garry63 if you just want a quick, cheap and easy way to see your battery voltage (voltage not capacity) without having to access batteries and use a multimeter you could connect an inline voltmeter in a 12v positive feed.
I've done this with my last 2 vans as the panel readout was way off.
I checked the voltmeter reading against a known accurate multimeter when first installed.
In my case the voltmeter reads 0.05v lower than my multimeter, so I know battery voltage is actually 0.05v higher than shown.
I do however now have a Victron smart shunt fitted and view that on the app on my phone.

 

[Stealaway]

Rubbish, a shunt will give you the state for charge whether the battery be in a state of charging or discharging at any time were as multi-meter will only give you a semi accurate reading when the battery is at rest.

What is a shunt reading to assess the state of charge if not the voltage?
I did say to a reading of charge.

 

[Spriddler]

I've got one of these...

Good enough as a double check of the control panel readout.

I use one of those and also charge my vehicle and hab batteries by plugging the charger in to the same permanently live cig lighter socket which saves having to access the batteries.
(I can select whether to supply the cig lighter from the vehicle or the hab battery).

 

[Two on Tour]

What is a shunt reading to assess the state of charge if not the voltage?
I did say to a reading of charge.

There's a bit more to it than that, time for you to do some Googling.

 

[Pausim]

What is a shunt reading to assess the state of charge if not the voltage?
I did say to a reading of charge.

A shunt may give you a voltage reading but it does not use voltage to calculate the % state of charge.

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[Stealaway]

A shunt may give you a voltage reading but it does not use voltage to calculate the % state of charge.

Just like this?

 

[headlight]

garry63 just remembered I wired the voltmeter direct to the battery terminals which in my set up was easy to do.
My voltmeter does exactly the same job as the one posted that plugs in a cigarette lighter socket.
However being connected directly to the batteries it probably gives a truer voltage reading than being plugged in somewhere in the 12v system.

 

[Pausim]

Just like this?View attachment 738163

Helpful as a rough guide on a good battery but not how a shunt works.

 

[Guigsy]

What is a shunt reading to assess the state of charge if not the voltage?
I did say to a reading of charge.

A shunt measures current at intervals of about a second. It can see current in or out of the battery. It adds up those amps to work out how many amp-hours you've used.

I can tell from my shunt that after 10Ah of use, the voltage is down to 12.2v. It's goosed! My FogStar lithium battery is going in at the weekend.

 

[headlight]

First picture is my control panel which just shows battery full which is pretty meaningless.
Second picture is the voltmeter which I fitted showing my batteries are sitting at 13.7v.
I have 200watts of solar which although it's raining and pretty dark here is holding my batteries on float.

 

[JockandRita]

I do however now have a Victron smart shunt fitted and view that on the app on my phone.

I don't have a shunt in place...................yet, but I did fit a Victron Smart Battery Sense, which I access via the App on my phone. The readings are about half a volt less than those on the panel.
I often check the reading when I get up early mornings, and before daylight starts waking up the solar panels.

Cheers,

Jock.

 

[headlight]

I just use my voltmeter reading as a quick rough guide as to how my batteries are doing as it's only a flick of a switch.
If I want to know exactly what's going on with them I use the Victron Smart Shunt and Smart Solar apps on my phone.

 

[headlight]

This is exactly what my batteries are doing.

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[SMB]

This works well and has several functions

 

[Guigsy]

View attachment 738190

This works well and has several functions

It does only tell you voltage though, no?

 

[SMB]

It does only tell you voltage though, no?

It also lets you test the cranking amps and indicates if the battery is charging etc, have a look at the spec on Amazon for a better idea of what it does. Once fitted you just leave it in place and access the information via an app on your phone.

 

[PhilandMena]

Ha! Ha! Love reading the contradiction from fun experts on this thread. Its very difficult to measure the true state of a battery when there is a load on it and voltage, unfortunately is not related to capacity. So its quite possible and happens often enough for a battery that is reading a good voltage to suddenly fail as it has no more capacity.
To establish the condition of a battery, a drop test needs to be done.

For anyone who is interested, the link below is a drop test I did on my Lead Acid batteies and I would suggest you pick it up from post #68

AGM OR LEAD BATTERY

First charge the battery fully and leave it to settle for an hour then:- For example if it's a 100a/h battery load it with a 5 amp load and run for 5 hours, this will represent a 25% discharge. (adjust load/time to suit the size of the battery) Disconnect the load and leave to stand for at...

www.motorhomefun.co.uk

 

[autorouter]

Just like this?

Battery charging is a chemical reaction, driven by the electric charge pushed in by the charger. The lead sulfate produced by discharging is gradually turned back into lead and lead oxide at the plates. Each bit of lead sulfate requires a definite amount of charge to turn it back into lead/lead oxide. If you measure the charge going into the battery, that tells you how much the reaction has completed.

The charge flowing into/out of the battery is measured in amp-hours (Ah). Using a shunt, with a built-in clock and computer chip, it is possible to calculate how many amp-hours of charge is going into or out of the battery. So it can keep track of how much charge is in the battery at any time. This is a very good indication of the state of charge of the battery.

Alternatively, it has been noticed that when the battery is at rest on a bench with nothing charging it and no load going out of it, the voltage can show the state of charge. That's what the voltage chart is all about.

However in a motorhome, especially if solar is fitted and there are constant small loads connected, that voltage can be very misleading. For example, the OP's picture of 13.7V doesn't tell you anything. It could be full, in the float stage. It could be very flat, and just ramping up to the absorption voltage. It could be a cloudy day, and 13.7V is the best the solar controller can manage. It's certainly not the 'resting voltage', which as the chart says doesn't go higher than 12.89V.

So all this means a voltmeter gives a reasonable indication in some circumstances, but a shunt measuring amp-hours is much better, and works even while charging and under load.

 

[garry63]

Wow heads mushed again.
All I want to know really is when I've been off grid when batteries need charging.
A quick simple,cheep way of knowing.
I don't have much confidence in the on board sargent ec200 control panels read outs