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!

[Crabbypatty]

Trimteric 2030rv. I have Trojan flooded batts and my first set, 14 years still going strong due to watching the % remaining.

Happy Trails

[sgfrye]

MrWizard wrote:

Click For Full-Size Image.

Maybe something like this
ALL INFO IN ONE place on one screen

i have had this one for a couple of years. bought off ebay, works great

[KMLsquared]

I use a $30 dollar Bluetooth unit from eBay. BM2 is the model. It has no display and must be viewed on a phone. The best part is I can check my battery voltage without getting out of bed. It stores up to 30 days of data that gets downloaded to the phone when within range. provides really nice graphs as well.

BM 2

I cant get the clicky to look right.

[Itinerant1]

3 tons wrote:
“ Derivative assumption, is like referring to an employee's time clock ticket to determine production rather than check the loading dock.”

Ha,ha, truly a solid candidate for quote of the year Sir!!

3 tons

I like that quote also. lol

[3_tons]

“ Derivative assumption, is like referring to an employee's time clock ticket to determine production rather than check the loading dock.”

Ha,ha, truly a solid candidate for quote of the year Sir!!

3 tons

[MEXICOWANDERER]

Once the battery electrolyte achieves maximum density the batteries are fully charged. Analysis by dirivities is pure bull pucky. Analysis of sealed batteries is verified only by hyper-exaggeration of charge parameters. There is a difference between "apparent full charged" and "verified full charged" The verified mode is needed to accurately zero amp hour transactions. Unless of course battery capacity and life are of no concern.

Verification (zeroing) is not appropriate for every cycle but should be performed every few weeks.

Derivative assumption, is like referring to an employee's time clock ticket to determine production rather than check the loading dock.

[time2roll]

My basic voltmeter resets to 100% every time. Never fails.

[MrWizard]

"Without plug ins, we also generally don't sit at float for hours upon hours to get your monitor back to 100%."

Don't need to be on float for hours & hours
Batteries don't really need floating in an RV that's in use, floating is too keep an emergency battery service from self discharge
Once batteries reach float, they are full
It's not the monitor that needs to come to 100%
In many instances, The monitor will reach 100% before the batteries are full, watching the charge rate is what is necessary with lead acid batteries,
Since lithium batteries have very little compensation needs, just count AmpHrs in and out, I think the one I using would work quite well,
If l had the $$ for lifepo4 I would get whatever monitor I thought was best for the job, be it Victron or something else

[3_tons]

The OP was asking about a “Good Monitor”....

Per 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. “

I can resoundingly second FWC’s off the grid experience, and the Victron 712 is also LiFePo4 compatible...It’s a matter of getting what you pay for...

3 tons

[deltabravo]

jornvango wrote:
What's a good monitor that I can install in my Casita to see the battery level throughout the day?

Victron BMV-712 like I installed

[MrWizard]

Capacity is a matter chemistry and chemical reaction increases with temperature,
And I do my best to not go below 70% SOC,
This morning I was at 83% capacity,
Colder weather will mean more heater runtime and lower SOC in the mornings,
But like I said batteries are in the heated basement,
My capacity does Not shift very much because of temperature,
Any drift/shift is the Perkurk? Effect (chemical reaction ) from evening and morning MW use,
Which BTW is also/more so, on your use
So if I use 80 AmpHrs over night, its really more, when I do the charging,
When the monitor says full but the charge rate is 3amps, no problem I'm in the high 90s SOC,
I can stop if I want or keep going
If the charge rate is high , 10 amps or more then I know I should keep charging until the batteries are full, goes to float or at least tapers to the right value,
Monitor saying full capacity, means the measured discharge has been returned, Does Not mean batteries at saturation level
You and I are trying to achieve the same thing
But your doing math with too many variables
While I watch for my recharge rate to reach the correct threshold

BTW this monitor has more setting that I do Not know the use of, and have left the values at default, there is probably one for recharge compensation, but the instructions weren't much help with that

[BFL13]

When I compare my "morning voltage" (close to resting) and its SOC with the AH count, that gives me a rough capacity. Since 12.1v is about 50% of whatever the capacity is, then if I am down 200AH, capacity is about 400AH.

I do a little math using the temperature vs capacity graph from my battery specs, and see if that is a reasonable number. There will be some more for battery age/usage.

My 460AH (as rated) might be 400AH on a cold morning, down 13% from rated.

If I did it the other way , using 460 as my capacity entry, and was down 200AH, the monitor would say I was at 57%. (the morning voltage would be 12.1v though-indicating 50%.)

By the time the monitor said 50%, it would actually be (230 down from 400) 42.5%.

On the recharge from actual 42.5%, I am unclear what the Ali would say. There is the business of whether battery temp is ambient or internal as it warms up from being recharged, and what temp to use with the temp vs capacity graph.

If the capacity is still lower, then the amps will taper to zero when it has its 200AH back (with heat loss allowance correct) before the AH counter gets its 230AH back. If capacity is closer to 460 again from internal heating, amps will run longer so the Ali comes out closer?

I do 50-90s with gen/charger so never get back up that high, and also get "progressive capacity loss" from repeated 50-90s. I can keep track of that doing my own math, but I don't see how a monitor could keep track of it all with a fixed capacity set for it.

In the summer with not so much temperature swinging (except in a desert) and closer to 77F, on solar getting to full most days, the monitor would not drift as much and also you have more chances to "zero" the AH counter too by getting to full so often.

I do find it confusing trying to imagine how different monitors would handle things.

[MrWizard]

I full-time my RV, I use the LP furnace, basement is heated, there is no need to change battery capacity numbers unless the batteries are degrading


Click For Full-Size Image.

Batteries fully charged
No need for me to worry about accuracy drift
I've said it here many times, I dont do 50>90 cycling of my batteries

[punomatic]

I have this one, and it does everything I need. I installed it with a DPDT switch so I can switch between reading during charging and during discharging.