How much juice left in my batteries

[Jofang]

We've recently changed from a Voyageur to a Hymer. The Voyageur had a display giving not only the habitation battery voltage but also the percentage of power remaining, which I found very useful. The Hymer only displays the voltage so I'd like to fit an instrument that could display the percentage remaining, same as the Voyageur. I anticipate this is a calculation relative to the voltage in the batteries but a display would be great. Any ideas how to do this? Maybe there are electrical boffins in the forum that could advise.

 

[Lenny HB]

Fit a Victron Smart Shunt or a Victron BMV712 either will give you all the info you will ever need.

 

[suavecarve]

Or if you go to amazon they have these things

Amazon product ASIN B09KLJXDSH
Take note of the delivery time, take note of the size of the amps for the shunt to ensure your batteries can be measured correctly

And far more importantly try to get the wires set up correctly or it will blow and you have to buy another one (so a friend told me)

 

[autorouter]

The Hymer only displays the voltage so I'd like to fit an instrument that could display the percentage remaining, same as the Voyageur. I anticipate this is a calculation relative to the voltage in the batteries but a display would be great. Any ideas how to do this?

There are two types of device calling themselves a 'battery monitor'. One type is a simple voltage measurement, that maybe does some kind of calculation to tell you the percentage remaining. It will normally be reasonably good, but totally inaccurate if there's any charging (solar, alternator etc)

The other type has a 'shunt' to accurately measure battery amps. It will keep track of the amps going into and out of the battery, and will be accurate even when charging or under load. The Victron BMV series, SmartShunt and NASA BM= types are this second type.

 

[berni109]

Most of the suggestion above are not inexpensive solutions. Search Ebay for coulomb meter and there are loads of options. Or memorise this table and if it's a normal lead acid battery dont run it below 50%

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[tonyidle]

Most of the suggestion above are not inexpensive solutions. Search Ebay for coulomb meter and there are loads of options. Or memorise this table and if it's a normal lead acid battery dont run it below 50%
View attachment 649922

A chart such as that one is accurate but only if the measurement is taken with the battery disconnected - not very convenient. It is also sensitive to temperature. A smart shunt & display (or phone) is accurate regardless of connections & temperature.

 

[Revolvor]

Most of the suggestion above are not inexpensive solutions. Search Ebay for coulomb meter and there are loads of options. Or memorise this table and if it's a normal lead acid battery dont run it below 50%
View attachment 649922

That table states " After 3 hours rest" It doesn't apply when the battery is under load.