Battery indicator on panel

[mmurr]

Every camper I have owned has a battery charge indicator that uses three or four little lights to indicate the state of charge. Everyone says not to discharge your batteries below 50%. Do the number of lights remaining have any correlation to battery percentage remaining. For instance when down to one light does that mean you are at 50% and it's time to charge?

 

[Isaac-1]

Those lights are nearly useless to determine state of charge, they are sort of like judging how full your gas tank is by when fuel splashes out when filling, and when the engine starts to sputter when empty. A digital volt meter is much better and only cost $10-$15, a shunt style state of charge meter is much better than a volt meter as it actually measures the amount of power in and out, these start around $50, and a good one coasts around $150

here is an example of a basic shunt style meter https://smile.amazon.com/AiLi-Voltmeter-Ammeter-Voltage-Motorhome/dp/B07FGFFHC6

 

[mmurr]

Thanks

 

[Mark_K5LXP]

The four LED's are nearly useless. Even a $20 battery monitor with a shunt will tell you way more.

The 50% rule is a bit specious. The bottom half of the battery works just as well as the top. With a better battery monitor you can ascertain your state of charge more precisely and not have to work around the limitations of a rule of thumb.

Mark B.
Albuquerque, NM

 

[Isaac-1]

The 50% rule is about maximizing life cycle, a battery drained down to 25% between charges will only last about 1/4 as one that is drained down to 50% between charges each time. Not the catch here is that you do get 1/3 more more watts out of each discharge cycle. So if you don't mind buying batteries more often go ahead and drain it past 50%, if you don't mind buying them very often go ahead and drain it all the way between charges.

 

[John From Detroit]

Do the number of lights remaining have any correlation to battery percentage remaining.

Generally speaking... NO. they MIGHT be accurate if there is absolutly NO load other than them on the battery but that condition almost never exists if it is even possible So NO

 

[Gary RV_Wizard]

Agree with the others. Typically the lights represent a voltage range of roughly 10v-13v, but the difference between any given number of lights is arbitrary, determined by the guy who designed the display. And measured at the display panel, not the battery. It's also inaccurate if there is any charging or load active on the 12v system when you read it.

Whether you need the superior data provided by a shunt monitor is a different question, depending on whether you want to invest in the personal effort to monitor and act on the data. Many people get along just fine using the system voltage as a rough indication of battery status, based on an actual voltage reading, e.g. 12.6v. You just have to recognize a few key points and understand the limits of what you are seeing.

1. 12.6v is a fully charged battery; 10.5v is "dead". 12.0v is about 50% capacity. These values are "at rest", meaning no load and no charging in effect.
2. You can't get a meaningful reading while the charger is active - it will always read 13+ volts. Disconnect shore power or turn the charger off to get a reading.
3. Without charging active, the voltage shown will display lower as the load on the system increases. It's reasonably accurate at zero load or very close to it, but even a couple amps of power draw (a single light, for example) will lower the voltage by a tenth or so. Eliminate as many loads as possible to get a better reading. The best way is using a digital voltmeter right at the battery with the battery ground cable removed.

Adding a basic digital voltage gauge inside the RV gives a more usable display than the light bar type, simply because a tenth volt difference is meaningful. Here's a cheap one:

0.56" DC 3-30V Digital Voltmeter Voltage Tester Gauge Green Bright LED Display Two Wires Volt Meter for Solar Battery Monitor Car Motor Panel Mount - - Amazon.com

0.56" DC 3-30V Digital Voltmeter Voltage Tester Gauge Green Bright LED Display Two Wires Volt Meter for Solar Battery Monitor Car Motor Panel Mount - - Amazon.com

www.amazon.com

Or a bit more elegant version with more data: https://www.amazon.com/Electricity-Monitor-6-5-100V-Multimeter-Voltmeter/dp/B08BCD5J81/?th=1

 

[Isaac-1]

If the idea of running a lot of wires to a display worries you Victron now makes a bluetooth shunt that will display to your phone. See

 

[Ex-Calif]

1. 12.6v is a fully charged battery; 10.5v is "dead". 12.0v is about 50% capacity. These values are "at rest", meaning no load and no charging in effect.
2. You can't get a meaningful reading while the charger is active - it will always read 13+ volts. Disconnect shore power or turn the charger off to get a reading.

Re: #2 - And disconnect all loads, and let the battery temperature stabilize, and adjust result for battery resting temperature - LOL... Battery State of Charge measurement is scientific and tricky and we have these debates too often.

Most simply as others have said get a simple voltmeter that plugs into the cigarette lighter. They are cheap on Amazon. You can get one with a couple of included USB ports.

That will tell you the voltage at the cigarette plug after resistance in the wiring is included and will usually be a bit lower than battery voltage.

Then - If voltage is above 12.6 you are probably in good shape when the charger is running - running loads will drop the bus voltage. Less than 12.6 and you are discharging due to loads exceeding charger (not likely), charger not on or charger failed.

When you get near 11V you are probably wanting to look for a charging source. Below 11V and high load devices (pumps) will start going inop. Incandescent lighting will be noticeably dim.

That strategy should keep most people advised of what's going on.