Most battery monitors work with an external shunt inserted into one of the main battery leads (usually the negative) such that all current flow in or out of the batteries pass through it. The display part of the battery monitor is able to convert the minuscule voltage developed across this shunt into a current readout so you know what is going in or coming out of your batteries at any time. Given this information they can also record the battery state-of-charge (SOC) usually as a percentage of fully charged (100%) as well as voltage.

The Smartgauge works in a unique and entirely different manner to produce similar SOC and voltage information but not current flow in/out of batteries. It achieves this with just a thin wire connection to the battery bank, so is much easier to fit. After connection it takes a short while to self learn your system after which it gives accurate SOC and voltage readings.

Designed for non-technical customers it may be the way to go if this gives you adequate info.

Given the price of batteries I would consider some form of battery monitoring essential to ensure they are not inadvertently abused.

mmmm To measure current or not to measure current and rely only on battery voltage. 

The parameter of a battery that we use is the current (Amps or Amp/Hours) the battery voltage rises and falls dependant on the battery type and to en extent the state of change of the battery. According to all the professionals that I have known over the years there is only one way to know whether a battery is fully charged and that is to know the specific gravity (SG) of the electrolyte when it was added to the battery and when the battery attains that SG it is fully charged. 

The voltage when charging a battery is, I am told, a factor of the battery’s internal resistance. Thus it is also related to the quality of the battery. Now if you have sealed batteries you cannot measure the SG, so they only thing you have got left is to count the current that you use from the battery and then count it back again. i.e. Using something like the BMV602 or similar. That does mean installing a shunt as the last item before the battery. Generally I have not found doing so to be a difficult task, all that is needed is to remove the (assuming Negative lead shunt) the negative leads from the battery fit a short battery lead going to the shunt and then connect whatever was connected to the negative terminal to the shunt. 

That then gives a measure of the current leaving the battery and the current going to the battery, and using the computer in the BMV602 etc the system will tell you if your batteries are fully charged or not. 

Oh thought for battery read battery bank if you have more than one battery in series or parallel 

I would not be without mine. The correlation between the BMV and the SG is very very close.

GM said
mmmm To measure current or not to measure current and rely only on battery voltage. 

 

The parameter of a battery that we use is the current (Amps or Amp/Hours) the battery voltage rises and falls dependant on the battery type and to en extent the state of change of the battery. According to all the professionals that I have known over the years there is only one way to know whether a battery is fully charged and that is to know the specific gravity (SG) of the electrolyte when it was added to the battery and when the battery attains that SG it is fully charged. 

 

The voltage when charging a battery is, I am told, a factor of the battery’s internal resistance. Thus it is also related to the quality of the battery. Now if you have sealed batteries you cannot measure the SG, so they only thing you have got left is to count the current that you use from the battery and then count it back again. i.e. Using something like the BMV602 or similar. That does mean installing a shunt as the last item before the battery. Generally I have not found doing so to be a difficult task, all that is needed is to remove the (assuming Negative lead shunt) the negative leads from the battery fit a short battery lead going to the shunt and then connect whatever was connected to the negative terminal to the shunt. 

 

That then gives a measure of the current leaving the battery and the current going to the battery, and using the computer in the BMV602 etc the system will tell you if your batteries are fully charged or not. 

 

Oh thought for battery read battery bank if you have more than one battery in series or parallel 

 

I would not be without mine. The correlation between the BMV and the SG is very very close.

I agree that a simple battery voltage measurement doesn’t give the whole picture, although if batteries are left to stand with no load for 30 minutes or so the voltage measured can give a very good indication of state-of-charge (SOC). Clearly this is not practical as an everyday means of determining their state and neither is measuring the SG of the electrolyte. 

What you dismissed in your post though is the Smartgauge as endorsed by Pete/perley. Although it only measures battery voltage, it has very complex algorithms within its display electronics that can sense most/charge discharge situations whilst they are happening and still give an accurate SOC with its self learning function which also compensates for battery ageing.

FWIW I have two shunt based Victron BMV600 battery monitors similar to yours, to display service and bowthruster battery banks. I wouldn’t be without the current display information as well as the rest, but knowing how to interpret the info is not for all. This is where the Smartgauge shines giving basic accurate info on battery SOC together with simple installation. 

Note also that the amp hour/SOC displays on shunt based monitors can quickly loose their calibration if the batteries aren’t regularly brought up to 100% SOC. They also require manual calibration to compensate for battery ageing.

I am very happy with my Smatguage though have not tested its accuracy.  From reports I have read it seems to be pretty accurate once it has “learned” your set up.  I would not be without it.

We have just been quoted £750 + vat to fit a batt monitor.

I really do not understand how anyone could quote £750 plus vat to fit a battery monitor. Even being generous it should not take more than 5 hours, so say £50/hr inc vat plus the monitor say at £150 inc vat £400 would be the maximum I would expect. In reality it should take less than two hours.

Batteries and Battery charging is part science and part black art Every manufacturer does it differently and it is difficult to get the detailed information about a particular battery, its charge voltages etc. Even the SGs are different. Periodically there appears on the market various bits & pieces that are supposed to improve charging, battery life etc. Remarkably a large number do little if anything to improve the lot of the owner of the batteries.

As for the Smartgauge I believe there is only one way to test it properly, that is not in a lab but on a boat running in parallel with something like the BMV 600 or similar. I would love to do it but the cost of the Smartgauge makes it an expensive test. If anyone knows a way of getting one either free or at a heavily discounted price to test over say two or even better four years then I would be willing to fit it to my boat and publish the findings. On the face of it the Smartgauge looks the ideal boat battery monitor but the blurb written about it is too much on the this is the perfect solution. Sorry the engineer in me is very unconvinced.

Clearly you are not going to be moved on this issue GM  I tried to give a balanced view of the shunt based v Smartguage systems. Many far more qualified than you or I vouch for the accuracy of the latter. It seems that solar charging can throw it out for a while though, but this pales into insignificance with the regular re-calibration of battery capacity with shunt based systems where the batteries are not regularly charged to a true 100% SOC. I feel I can afford to say this as I have two shunt based monitors. I understand the Smartguage designer is working on a version that includes shunt/current measuring as well.

@richardhula mmmm Interesting what do you know of my qualifications, experience, knowledge or how long I have been around boats batteries etc, I find your your comment “far more qualified than you” quite insulting and patronising.

I had heard rumours that a shunt version was muted but not that it was actually about to pop. When I asked the question why if the existing is so good why add a shunt, there was a total silence. I really think the case for the needing to measure the current (adding a shunt) has just been made. Thank you richardhula

Like all measurements and measuring equipment, calibration is the key. In the case of battery monitoring if you can get the necessary information from the Manufacturer then that calibration can be that much more accurate and stable.

Matty Smith installed my solar panels and Smartguage.  Very reasonable rates and excellent work (and a very friendly guy).

Website http://oldfriendscanalservices…..eebly.com/

I have no connection other than as a friend.

GM said
@richardhula mmmm Interesting what do you know of my qualifications, experience, knowledge or how long I have been around boats batteries etc, I find your your comment “far more qualified than you” quite insulting and patronising.

I had heard rumours that a shunt version was muted but not that it was actually about to pop. When I asked the question why if the existing is so good why add a shunt, there was a total silence. I really think the case for the needing to measure the current (adding a shunt) has just been made. Thank you richardhula

Like all measurements and measuring equipment, calibration is the key. In the case of battery monitoring if you can get the necessary information from the Manufacturer then that calibration can be that much more accurate and stable.

Apologies GM I did not mean to insult or patronise. My comments were based upon the fact that you dismissed one popular and easy to fit technology on the grounds that you found it inaccurate. You also quoted my comments out of context. 

I just wished to present a balanced view on this issue and point out the caveats with various systems and how one doesn’t suit everyone.

I don’t think I’m speaking out of turn when I suggest that most just want a fuel gauge for their batteries. As MikeEaves says boats aren’t rocker science so why make them so.

Smartgauge for me  

I just open the cupboard, press the button see what % is left, look out the window to see if there is enough sun for solar and bung the geni on if not and go and do something more interesting.

It only took me an hour to fit and most of that was woodwork mounting the display. 

My bats cost well under eq £800! About £370 for five and that was from midland swindlers! 

I try not to use the engine for charging as it uses 1.5l/hr and costs about 30p/hr for a basic 250hr service.

To Paul B,

No experience from on narrowboats but lots of research and previous knowledge of all things mechanical/electrical from my time in the RN.

General facts – Generator will use less fuel than your engine for the same amount of power transferred to your batteries.

                    Generator will not need to be serviced as often.

                    Currently the generator qualifies for the cheaper rate of diesel taxation. May need separate fuel tank soon though if EU get                       their way.

                    Generator needs space, a valuable commodity on a narrowboat. This can never be regained.

                    It will take a long time, as in years, for the savings in running costs to be equal to the extra original purchase cost of the                           generator system. 

                   Your battery bank will benefit from being fully charged up but the charger controllers as run by either your engines alternator                       or your generator while possibly being able to do the type of charging required are not capable of reducing the effect of light                       load running on either.

                    A few solar panels will soon pay back the initial investment on this matter. Fitting an mppt controller will also gain you approx                       25% extra power from your panels as well. 

                    If you moor up in a marina and you connect to shore power it will certainly be a cheaper option (as a means of charging your                     battery), obviously the costs of that mooring and electrical charges have to be considered.

The real question you need to ask yourself is what will your be operating cycle be? how many hours per day cruising/stationary, how long between marina berth stays, how much power will you use when not running the engine. Can you modify your power needs? e.g. less tv watching. How much are you willing to spend on batteries.

Everything about living on a narrowboat comes down to one word COMPROMISE. 

All of this needs to be considered in order to get the right decision for you and your boat but the general facts as above will hold true.