How to monitor battery state of charge

[rfloyd99]

Based on advice I recently got here I upgraded my TT battery setup to two golf cart batteries. I won't be upgrading my converter or any other parts of this system (or adding solar) at this time, although I got lots of good advice on that for later.

My goal is to increase our ability to boondock for a few days here and there on our upcoming six month trip.

One piece of advice I would like to follow is to install a monitor so I can know when to put a charge in the batteries before running them down farther that is prudent.

I've looked on Amazon but don't know enough to decide on a product. (I prefer Amazon, walmart or an auto parts store since we're leaving next week).

Can someone please tell me what I should be looking for as a monitor, and also what readings will indicate that I need to charge up soon?

As always, thanks for the great input available here.

[Harvey51]

I see the phone adds the ability to graph over time, a very nice feature. Kind of nice to have a dedicated display for all to see, though.

I wonder if batteries will ever be sold with a built in monitor showing the state of charge by one means or another.

[RJsfishin]

Well lets use logical thinking here. It probably doesn't care what size the battery is.
Therefore if multiple batteries is just one bigger battery, what do you think ?

[DiskDoctr]

MrWizard wrote:
https://www.amazon.com/Wireless-Multimeter-Bluetooth-Battery-Monitor/dp/B0184XHL1K

wireless Bluetooth battery monitor, mounts at battery monitor with your smart phone or tablet

How would that work with multiple batteries? One per battery?

[MrWizard]

something NEW, that will interest some of the techies here

https://www.amazon.com/Wireless-Multimeter-Bluetooth-Battery-Monitor/dp/B0184XHL1K

wireless Bluetooth battery monitor, mounts at battery monitor with your smart phone or tablet





approx $130, but much easier to install

looks like it can be used with OR without a shunt, depending on the expected max load or charge amps

i would use the shunt

In Stock! Easy installation, free app on Google Play.
Completely weatherproof and designed to be permanently connected to batteries in any environment.
Extends battery life by showing you instantaneous power draw.
Shunt is optional! An internal current sensor measures up to +/- 30 Amps.
Diagnose battery problems such as unwanted battery drain.

available thru amazon

[Harvey51]

When using the voltmeter remember it just shows the charging voltage when charging and only gradually decreases over a few hours after charging ceases so you cannot find the per cent of full charge for a few hours after any charging. Also, drawing current from the battery decreases its voltage adding another complication to the voltage method. I wasted my first set of batteries relying on the idiot lights which use the voltage method.

This $29 battery monitor always shows the percent of full charge accurately and has positive reviews on this forum. The 25 amp version has worked very well for me for several years. Ebay.com battery monitor

[DiskDoctr]

Someone posted this link recently.

Here's a pic

[pianotuna]

I would go with the volt meter, and as time permits I'd calibrate it to the state of charge figures from a hydrometer.

[doughere]

In your next week time frame: I'd suggest a "cigarette lighter" plug in voltmeter and a hydrometer both available from Amazon. You might be able to find them locally. O'Reilley Auto Parts used to have a hydrometer for less than $10, and I think I've seen the plug in voltmeter in auto parts stores.

There are very good systems available, but I don't think you have time to investigate and install them now.

2 good GC's should give you a couple of nights run without trouble unless you use a lot of heater fan.

Regards,
Doug

[KD4UPL]

A true battery gauge will involve a shunt to measure the current in and out of the battery. You program the device for the AH of your bank and it will keep track of how many amps have gone in and out over time. This is a far more accurate than a simple volt meter. A battery's voltage fluctuates based on whether it's being charged or discharged when the volt reading is taken.
One simple and fairly inexpensive battery gauge is the TriMetric. They make several different model, the TM-2030-RV would be the one I'd look at. Link10 is another gauge that is worth considering.
If you do plan to ever get a nice inveter/charger most manufacturers also make a battery meter. They typically will plug into the communication bus of the inverter/charger and allow you to see the battery level on the same display keypad. Magnum, Outback, and Xantrex all offer these; I think Victron has one too.
A hydrometer is really the best way to know how your batteries are doing but that can get messy and is best left for occasional check ups at home. A simple volt meter, or worse yet the idiot lights that come with most RVs, is a very simple, inexpensive, and rather inaccurate way of trying to determine battery state of charge.

[time2roll]

Leaving next week? Simple voltmeter is fine.

Plan to run the generator for a couple hours starting the second day.
12.4 to 12.0 is time to recharge with increasing urgency as you approach 12.0 volts.

The 12 Volt Side of Life

No way would I take a hydrometer camping.
Not sure how the hygrometer on your weather station will help.

[RJsfishin]

Yes, I'm sure he wants to be messin w/ a nasty hydrometer every day while on a camping trip.

I can tell you an easy fool proof way to monitor, w/o a monitor.
Listen to the water pump,....if you notice a noticeable slow down in pump speed, along w/ noticeable light dimming, it time to charge.

[GordonThree]

x2 for the Hygrometer for flooded cell...

or current integration (coulumb counting) for any battery type

[VoodooMedicineM]

Get a battery hydrometer.

[donn0128]

You can find 4 digit digitwl volt meters at places like ebay reasonable. Thats what I did plus a momentary push button switch and I can see the voltage at a glance.