What battery state of charge meter do you use

[Roadtripp]

I’m curious to hear what battery meters you are using for your solar, house battery, and might as well include starting battery if you don’t use the stock one ? 
 I’m getting around to installing a battery meter on my solar house battery. I tried a fancy one I got used cheap. It worked for a minute then quit. I saw a tiny spark where the wires came loose. My bad. I tested the voltage leads coming from the shunt negative and battery positive . It still has voltage. So I’m wondering what to order? 
 After reading posts by Sternwake and others I’d like to read more accurate data from my system. Has anyone had good results with a cheap one. Thanks

[Flying kurbmaster]

I know it is not ideal nor is it accurate but I use so little power that I use a simple volt meter, with a switch to turn it on and off so it doesn’t draw all the time and that way i can also see when the alternator is charging it . It rarely goes to 10 volts mostly it’s lowest is 11 it goes as high as 14.5 when the alternator is going and a bit less on the solar at full sun.

[B and C]

I use a Trimetric 2030 RV to monitor my batteries. It shows amps in and out as well as voltage and percent of charge on the house batteries. It has a separate lead that goes to the starting battery to show voltage for it. I wouldn't be without it. It does require a shunt and it sounds like you already have one.

http://www.bogartengineering.com/product...trics.html

Shop around for best price.

[sternwake]

In 2007 I installed a Blue Sky SB2512i solar charge controller, and am IPN Pro remote battery Montor, which also allows one to change the charge controller parameters.

I trust its AH from full screen to be about 90% accurate, about 85% of the time.

Some people will simply believe it to be 10% accurate 1005 of the time, but the truth is they need to be set up properly, calibrated, and reset every so often when the batteries are truly known to be 100% charged.

True full charge on flooded batteries requires a temperature compensating hydrometer and a charging source able to hold the batteries at a high enough voltage for long enogh for the specific gravity on all cells to reach the predetermined maximum expected number.

Since the battery monitor is not sampling the strength of the electrolyte, but merely counting amperage into and out of the battery, and making assumptions at te efficiency ar which the battery is accepting or delivering its amperage, it is basically guessing as to its charge level.

but the battery monitor is a wonderful learning tool, but the person who believes it 100%, with no corroboration that when it says the batteries are full, that they ctually are, well this is unwise.

as far as battery monitor products, all the good ones are in the 200$ range.

Newer Cheaper ones have come on the market more recently, and I have NO experience actually employing them myself and have No idea how accurate they are, nor their features, and I will not, until I own and set one up and use and monitor it and compare it to known accurate ammeters.

This one sends a blue tooth signal from the amp measuring sensor to the display:

https://www.ebay.com/itm/183247639501

Again, no personal experience with this product and it is not personal recommendation and I am not vouching for it.

There are other similar ones that use a Shunt and wires to the display.

Do note some shunts are 50Mv and some are 75Mv, some are rated at 100 amps, some are 500 amps. You do not get to mix and match shunts unless the specs are the same.

Read these articles:

http://www.pbase.com/mainecruising/battery_monitor

http://www.pbase.com/mainecruising/progr...ry_monitor

I think a lot of people would do very well at learning how to read their battery level and over time, its condition, with a 3 decimal place voltmeter.

I do have this product ad it is neat watching that 12.807v turn to 12.798 turning on another LED light.

https://www.amazon.com/DROK-0-33-000V-Digital-Voltmeter-Accuracy/dp/B00CJR9QB6/ref=sr_1_7?ie=UTF8&qid=1545072996&sr=8-7&keywords=5+digit+digital+voltmeter

I was wishng it had a little calibration potentiometer but it turned out to be spot on with my trusted Digital multimeter.

If one watches an accurate 2 or 3 digit voltmeter through many recharge or discharge cycles they will get a great Idea of just where their battery is and how it is performing. Too many people assign a voltage to an exact specific state of charge, and this can only be accurately done when the battery is well rested, not havng seen any loads or charging sources for many hours.

While voltage is not a specific indicator to exact state of charge on a battery in use, it is still a very valid tool, but when one can see how many amps are flowing into or out of the battery at that voltage, the picture becomes much clearer.

The battery monitor is counting those amps, and will give a % and an amp hour from Full, but it assumes a lot and can be wildly inaccurate. How does one test this, By a hydrometer and a voltmeter and an ammeter. I look at my battery monitor now, but I do not bother at all, ever with the % screen, and the Ah from full screen is interesting when discharging, especially after freshly resetting rezeroing it when I know the battery was full, but I determine full by how many amps the battery is accepting at absorption voltage, and when it falls to 0.5% of battery capacity, does the battery monitor agree?

Well it does, about 85% of the time, and If I have not reset it recently, i do not trust its reading. I've seen it read 1005 full when the battery was at least 12Ah from full, and I've seen it read 12Ah from full when it was stuffed full.

Trust, but verify. Blind trust = foolishness.

[Flying kurbmaster]

Oh yeah i forgot I also have a very inexpensive hydrometer which I rarely use. Thinking about it now I use to use the volt meter and the hydrometer but now I guess all I do is look at the charge controller.

[sternwake]

My issue with many charging sources, is simply trusting the charge controller to hold absorption for long enough.

Long enough when the battery is new and healthy, is not adequate when the battery is aged and te deeply cycled battery regularly returned to 100% will last much longer than the same battery regularly returned to only 98% charged, and that last 2% can take 90 or more minutes held at absorption voltage.

The solar charge controller might show amps it is producing, but some portion of those amps are going into powering loads when one is wanting to know how many of those amps the battery is accepting.

BUt picking nits gets old too. Once one has seen several hundred cycles one can get a great sense of where the battery is by a voltmeter alone, but the Hydrometer can and will reveal that the assumed full charge, corresponds to 1.260, and getting elecolyte back upto 1.275 required voltages upto as high as 16.2 for possibly a few hours. after this true equalization full charge, one can reset their expectations for voltage held under loads.

[B and C]

This is why I like solar charge controllers that are shunt based where you can set end amps instead of relying on a timer. It only sees amps going to the battery, not any loads that the solar panels are running without the battery.

[WanderingCanuck]

I didn't catch what type of batteries you have, but if you have deep cycle flooded lead acid then it's pretty hard to beat a battery hydrometer for price and accuracy.

[Roadtripp]

Thanks Folks,
Omg, this must be sooo confusing to folks not inclined towards numbers and logic. I am beginning to wrap my head around it as I got the basic understanding of non linear, inverse proportional, algorithmic relationships. I’m just slow is all. I’ll be getting to know my motorhome Renogy Gel cell batteries better after being away almost a year. The voltage floated on solar for better part of a year right after installing them new. Seem a bit weak now but I’ve not done testing them yet. Maybe they were very cold outside which reduced capacity? I’ve been using agm batteries on my van solar energy system while away from the Motorhome . They were used to a unknown extent agm batteries when I got them so it’s been challenging to know how to even guesstimate state of charge. But I may have got lucky as the low voltage shut off on the inverter hasn’t triggered yet. After reading the:
http://www.pbase.com/mainecruising/progr...ry_monitor
link Sternwake provided I’m inspired to try doing an approximate capacity test and gather together a good multimeter and capacity meter. A friend mentioned that Home Power magazine printed a chart years ago to enable doing approximate capacity calculations. I’ll look for that chart. Oh, he said Home Power is stopping publication by the way.
The above mentioned link talks about a new meter, the Balmar Smartguage

It claims to learn. Is this the machine learning I hear about in the coding world? Maybe that will be the answer to battery guessing now that machine learning is where the rubber meets the road?
I can hear you saying that experience and a good DMM with ones batteries is the same if not better than a super smart meter with machine learning. I tend to agree and want to learn but I know some folks who would certainly not.

[sternwake]

The Balmar smart meter is said to be quite good at giving approximte state of charge during discharge, but not so much when charging.

but if one can see the amperage the batteries are accepting when charging at absorption voltage, one can get a good idea of how much further they need to go, but how much longer that full charge will take, for amps to taper to the required level at absorption voltage, is dependent on the battery condition and temperature and other factors.

http://www.pbase.com/mainecruising/smart_gauge

The renogy Gel cell batteries you mention, are these actual Gel batteries?

Often a battery on float for a long period will seem to be lazy and not perform as it should, but a deep cycle followed by a relatively high initial amperage can wake them up. You must b careful with actual Gel batteries not to exceed a certain amperage or voltage and consider battery temperature in that too. Actual well treated Gel batteries are the best deep cycle batteries, the issue is their specific recharging requirements are not easily met, especially when there is a an alternator in the equation whose voltage regulation cannot be tampered with.

A somewhat accurate capacity test it to load the battery at the 20 hour rate, which would be 5 amps for a 100Ah battery, for just 10 hours, and ten remove the load and watch the battery voltage rebound. If it is around 12.2v after an hour then the capacity is likely still around 100AH, but if it only rebounds to 12.08 then you might estimate tose 100Ah is now 87AH or so.

This 10 hour capacity test at the 20 hour rate is nowhere near perfect, but you can at least compare the same test to future test using the same loads for the same durations trying to keep the variables the same.

The true capacity test is a 5 amp load for 20 hours and hoping it does not fall below 10.5v, but attaining and maintaining a true 5 amp load as battery voltage declines, is difficult to achieve, and the battery is supposed to be held at 77f throughout the test, which is also not easy to achieve.

You can make your own capacity tests simply by powering a load when the battery is known to be full, and seeing how much the voltage drops. The starter motor is ~140 amp load, an Aircompressor can be 16 amps, an Inverter powering a 100 amp light bulb...... Once you have an ammeter, and a good voltmeter, any discharge can be considered a capacity test, just keep the variables the same or as close as possible, and then one can see if an extensive top charge changes the results for the better, or the results are similar after another 50 deep cycles.

Or you can just use the freaking batteries and replace them when they no longer have enough capacity meet your needs, and not worry about any of this shit. The price of a lot of these components required to perform tests and measure things and charge ideally or close to it, can buy a good amount of lead.