What's a good battery level monitor?

[jornvango]

What's a good monitor that I can install in my Casita to see the battery level throughout the day?
Ideally a monitor that draws minimal power since we boondock frequently.

When we're camping in an RV park with hookups, I'd like to see once in a while how much voltage the converter is sending to the battery.

While boondocking, we hook up our portable solar panel and I can see the battery level by going outside to look at the solar panel controller, but I'd like to have a monitor inside the Casita.

Thanks!

[BFL13]

I get it now, I think! Does the ali show the amps still going in and tapering while the AH counter is frozen at zero when it thinks you are at 100%? When it gets dark and amps go negative, does the 100 start to go down then too? (kind of an auto reset?)

What about charging efficiency? The Trimetric has default setting for that (which you can adjust) ISTR 94% ? Anyway, that means it records the correct amps but adjusts the AH by that amount when charging-but not when discharging-, so that if the charging efficiency (allowance for heat loss) happens to be correct, AH back in will equal AH out. Since that allowance for heat loss will be off by whatever amount, your counter will "drift" and need to be reset.

The capacity entry that is "full" needs to be corrected for temperature and battery condition, so the %SOC will be wrong just from that. An AGM loses 15% capacity at 32F compared with its rating at 77F, eg. Do you re-enter your capacity according to average ambients when camping? Battery age and usage matter too. Say your battery loses 5% a year and you have 3 year old batteries (down 15%) at 35F (down 15% from that.) So what is your capacity for 100% that your monitor is using?

I prefer to have the actual approx capacity at the time worked out and figure out the SOC myself from the AH count. I just can't see how the monitor showing a percentage SOC can be believed, so I don't even have that displayed.

That is also where voltage /SOC is misleading--- the capacity can be down but the voltage per SOC is still close to valid. You can be at near full voltage with a smaller capacity. So the AH counter is valuable as a cross-reference to see if they "match" for SOC.

"Percentage of what?" has to be asked.

[MrWizard]

If you keep charging past when the monitor says 100%, then your AH counter will be out of whack and needs to be reset to zero once you do get to True Full.

NO !
My monitor and most other ones stop adding amps to the capacity value when the amps returned equal what was removed and set value is reached
Charging does Not Stop, but count does not increase beyond the set value
I think you are thinking of your way of a minus value from zero for amp hrs used then recharging to a plus value larger than zero to compensate and ensure you are at or near full,
Confusing what your display shows, with what is the normal operation of my system

[FWC]

This only works if you sit at float voltage for long periods of time. The current into the battery at float is typically only 1-2% of capacity, so if the monitor is off by 10%, it would take 5-10 hours at float to catchup. This may work for you, but not for folks that don't plug in every night, like the OP.

[SJ-Chris]

BFL13 wrote:

If you keep charging past when the monitor says 100%, then your AH counter will be out of whack and needs to be reset to zero once you do get to True Full.

I don't know how your battery monitor works, but I can share with you how I believe my Aili battery monitor works...

On the Aili monitor, you set the total AH of your battery bank and you also tell the monitor when you are charged to 100% initially to set it up. As you use your battery, your AH and % full value starts declining based on how much is draining out of your battery. Then when you are charging your batteries, the battery monitor will climb it's way up to 100% status and 100% AH as current is flowing into the battery. Once your monitor gets to "100% full" your AH will also be listed as 100% of your total battery bank AH. It cannot go any higher.

Now let's assume that in actuality you are NOT at 100% SOC even though your battery monitor says that it is. With the Aili, if you continue charging (either through solar or generator or plugged in or your alternator), your battery monitor will still just say 100% full (and AH at your max) as it continues increasing the true SOC until eventually you actually are at true 100% SOC. There is no resetting necessary on the AHs or the total capacity %.

Another way of thinking about all of this.... Let's assume that your batteries are at 50% SOC. 50% full. And let's assume you have 200AH total in your battery bank. Let's say you program your Aili battery monitor and you tell it that your battery bank is 200AH and your are currently at 100% fully charged (even though you are in actuality only at 50% SOC). If your next step was to plug in your rig for 10 hours charging the batteries (or driving for several hours while your alternator charges your batteries) your battery monitor would say "100% full" and "200AH" during the entire time. Eventually, your batteries WOULD BE at 100% and your monitor would now be showing you the proper SOC. No need to reset/etc.

And as mentioned before, at any time you can use the monitor to display the battery voltage to tell you where things are at.

Hope that makes sense.
-Chris

[FWC]

It is not just theory. For many of us who don't plug in, you can get several partial charge cycles in a row (several days of non optimal solar for example) and as a result your SOC can be significantly off. Without plug ins, we also generally don't sit at float for hours upon hours to get your monitor back to 100%.

Yes you can make it work without these conveniences, but you have to remember when the last time you were on float for multiple hours, or try and check the battery voltage when you know things are at rest.

My point was that the good battery monitors deal with this, and you can be fairly sure when you glance at the display that the number is pretty close to reality. Cheaper monitors are a compromise.

I use lithium batteries, so the voltage doesn't tell me much about the SOC. However I have a good battery monitor that is correctly programmed for my batteries, and I can trust it.

SJ-Chris wrote:
Regarding the drifts and possible inaccuracies due to a variety of behavioristics of charging and/or the batteries themselves....

I can see how IN THEORY you could have an issue if every time you charged your batteries you immediately STOPPED charging once your monitor said you are at 100%. If you were in fact not 100% full (...let's say the true SOC is only 95% even though your monitor incorrectly says 100%) and then you used your battery down to 50% as stated on your monitor, you would in actuality only be at 45% SOC. Then if you charged back up to what you thought was 100% and immediately stopped charging once your battery monitor says you are at 100% but in fact if it once again fell short you might only be at 90% true SOC. If you repeated this many times in a row, then I can see you'd have a problem. (drift)

Perhaps a good rule of thumb would be to make it a habit to continue to charge your batteries for a little while beyond the time when your monitor says you just reached 100%. Or, if your monitor shows amps going into your battery while charging, you can get a sense that way as to how much "charging" is still happening once your monitor reaches 100%.

This "drift" problem gets fixed/reset anytime you do have a situation where your charger stays on/active for a long enough time after your battery monitor says you are at 100%. For example, if you do find yourself plugged in at a campsite and your monitor reaches 100% (even if your true SOC is less then 100% because it has been drifting) while you are sleeping and then continues getting you to true 100% until you unplug. Or, if you are driving from one destination to another and your alternator is charging the battery...if your monitor gets to 100% (when your batteries are actually at less than 100%) the batteries will continue to get closer to 100% as long as you are driving. This "erases" any of the drift delta that might have built up.

Also: Most battery monitors tell you the Voltage it sees on the batteries. From most 12v SOC charts you can see that 12.06v resting voltage corresponds to 50% SOC. So if you ever see your battery resting voltage at 12.06v REGARDLESS OF WHAT YOUR BATTERY MONITOR SAYS percentage-wise, you should charge your batteries. Likewise, when your batteries are truly fully charged to 100% they will likely read ~12.7v at rest. If your monitor says it is 100% full but your batteries are only at 12.4v or 12.5v then you should continue charging until you get all the way up to 12.6-12.7v at rest. If your batteries never get there, then there is likely a problem with your monitor voltage reading (you can test by putting a voltmeter directly on the batteries) or a problem with your batteries.

-Chris

[BFL13]

Alternator charging should also pass through the House batts' monitor's shunt. The usual wire from the neg post to the frame for "grounding" is taken from the neg post and now goes on the shunt with all the other neg wires. Then there is one fat wire from shunt to neg post.

If you keep charging past when the monitor says 100%, then your AH counter will be out of whack and needs to be reset to zero once you do get to True Full.

The Trimetric default is to reset to zero when charging stops. It has no real idea what the true SOC is then. I don't like that whole business of how the Tri is supposed to work and the definition of "full" it uses. I do love my Tri though! I just use it "my way" 🙂

If you have solar and a Tri, it shows "charging" till it gets dark and then amps go negative again so it acts like you are full and resets. So they say to disable auto reset, which works great. Now it keeps counting up and down until sometime you manage to get the batts to True Full and you reset the AH counter to zero yourself.

I have read the Victron manual for how it works, but can't understand it. I would have to have one and see what goes on. Anyway, whatever monitor you have, you must stay on top of it and not let it mislead you.

[SJ-Chris]

Regarding the drifts and possible inaccuracies due to a variety of behavioristics of charging and/or the batteries themselves....

I can see how IN THEORY you could have an issue if every time you charged your batteries you immediately STOPPED charging once your monitor said you are at 100%. If you were in fact not 100% full (...let's say the true SOC is only 95% even though your monitor incorrectly says 100%) and then you used your battery down to 50% as stated on your monitor, you would in actuality only be at 45% SOC. Then if you charged back up to what you thought was 100% and immediately stopped charging once your battery monitor says you are at 100% but in fact if it once again fell short you might only be at 90% true SOC. If you repeated this many times in a row, then I can see you'd have a problem. (drift)

Perhaps a good rule of thumb would be to make it a habit to continue to charge your batteries for a little while beyond the time when your monitor says you just reached 100%. Or, if your monitor shows amps going into your battery while charging, you can get a sense that way as to how much "charging" is still happening once your monitor reaches 100%.

This "drift" problem gets fixed/reset anytime you do have a situation where your charger stays on/active for a long enough time after your battery monitor says you are at 100%. For example, if you do find yourself plugged in at a campsite and your monitor reaches 100% (even if your true SOC is less then 100% because it has been drifting) while you are sleeping and then continues getting you to true 100% until you unplug. Or, if you are driving from one destination to another and your alternator is charging the battery...if your monitor gets to 100% (when your batteries are actually at less than 100%) the batteries will continue to get closer to 100% as long as you are driving. This "erases" any of the drift delta that might have built up.

Also: Most battery monitors tell you the Voltage it sees on the batteries. From most 12v SOC charts you can see that 12.06v resting voltage corresponds to 50% SOC. So if you ever see your battery resting voltage at 12.06v REGARDLESS OF WHAT YOUR BATTERY MONITOR SAYS percentage-wise, you should charge your batteries. Likewise, when your batteries are truly fully charged to 100% they will likely read ~12.7v at rest. If your monitor says it is 100% full but your batteries are only at 12.4v or 12.5v then you should continue charging until you get all the way up to 12.6-12.7v at rest. If your batteries never get there, then there is likely a problem with your monitor voltage reading (you can test by putting a voltmeter directly on the batteries) or a problem with your batteries.

-Chris

[phemens]

dieseltruckdriver wrote:

phemens wrote:
I like the Victron 702, with Bluetooth so you can monitor from your phone.

I really like my Victron 702 also, but the 712 is the one with bluetooth, unless you add a dongle.

You're right, I have the dongle, thanks for the clarification!

[StirCrazy]

this is the one I recomend. accurate, simple and deicent shunt.

https://www.amazon.com/AiLi-Battery-Monitor-Voltmeter-Motorhome/dp/B07CTKYFTG/ref=pd_sbs_328_3/130-7...


Steve

[MrWizard]

This is the seller elite.element on EBay, I bought from, and the power monitor, he is in Walton Ky,,
DC battery power monitor

It's all over ebay for less $$$ , but shipping from China sellers,
I think he was the first one to bring it to the USA


Click For Full-Size Image.

[MrWizard]

Charging inefficiency is a problem that never goes away with any lead acid battery, and only gets worse as the battery ages,
That's why an auto reset monitor, is not as important to me , as knowing my batteries and system,I know by looking at the charge amps near the end of cycle, the monitor already says 100%,

What's important to me, is the discharge count and the SOC from my use, so I know how many Amp hrs were used, Capacity (50% ,70%, 90% ?) right now
I know whether I must charge right away or have sufficient unused capacity to hold me until later in the day,
I do not know how many Amp hrs recharge it takes to replace 100 Amp hrs used, 5 more, 10 more, 15 more ??
And it's been many years since I even attempted to find out, when I tried I had (2) amp counting power meters wired in series with the house batteries in a different MH, identical meters,they only counted one direction, so I installed them in reverse to each other, one only counted discharge , the other only counted charging , I reset them each day at the end of that days recharge, I don't remember the numbers, but the recharge to full, goto float, was more than I expected, no MW no coffee maker , a 300w inverter for the laptop, tv, and phones, it was about 2005 I think, maybe before then
This monitor I have now, is the best one I have used, the most useful,the most info
I will try to find the brand/model info, it's been almost 3 years, and I think the seller was in kentucky, I'm thinking this was on eBay,
BTW the display/control module (in the picture) is powered 5v usb, and is wireless,
The brain module and the Hall Effect Sensor are located at the 198 ampHR Deka 4D AGM that is one half of my 400 AmpHR battery bank, there is No Wiring connecting the 2 modules, I can move the display any where in the RV, without changing any wiring

[FWC]

The issue with many (most?) of the cheaper battery monitors is that they don't resynchronize with a fully charged battery, and they don't account for charging efficiency. As a result they can drift well away from the true SOC over time, which can provide confusing information.

Better monitors will detect when your battery is fully charged (based on the charger switching over to float) and will reset the SOC back to 100% and will also account for the fact (with lead acid) that you need to put 21A back in to replace the 20A you took out.

[SJ-Chris]

I recently posted this:
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30168196.cfm

Aili battery monitor is what I am using and I love it. And it's only ~$45 on Amazon. Gives you all the info you probably want/need. Doesn't connect to your phone, but it's way less expensive.

[FWC]

The OP did ask for a 'good' meter not necessarily a 'cheap' battery monitor. For a good meter, you can't go wrong with the Victron 712 (with a display) or the Victron SmartShunt if you are happy to look at the data on your phone/tablet/laptop. If you would prefer 'cheap' then any of the many no-name panel voltmeters or current shunts will work.

[rlw999]

obiwancanoli wrote:


Go to www.amazon.com, type "Victron 712" in the search box at the top of the page....

That's a good way to find the Victron 712, but @HomelessByChoice was asking about the picture that @MrWizard posted, which is not a Victron.

I'd like to know too.

I found what I think is a product link for it based an image search, the DROK Automotive Multimeter, but that link leads to an error page, so apparently it's been discontinued. But Drok sells many other inexpensive meters, so I'd still like to know if @MrWizard has been happy with their products.