Battery Voltage

[Blown284]

Hi everyone. Starting to consider battery monitoring solutions. I have two huge (8D type) house batteries (AGM type) and are showing 13.22 (battery 1) and 13.25 (battery 2). Is there an easy way to figure out that 13.x voltage = % of battery?

Any insights would be greatly appreciated.

Thank you.

 

[hughespat57]

Using basic voltage to determine State of Charge is always a bit problematic.
Right now you are likely seeing the AC charger voltage.
So to get a good idea of SOC you need to turn off the AC converter/charger and then the batteries will still have a "surface charge" left from the charging. So you need to run something like a blower for a few minutes and then check voltage.

A BMS will normally include a current shunt so the meter can adjust its algorithm based on all factors.

typical AGM chart

 

[my3sons]

Download this image onto your phone and be in the know.

 

[Blown284]

Using basic voltage to determine State of Charge is always a bit problematic.
Right now you are likely seeing the AC charger voltage.
So to get a good idea of SOC you need to turn off the AC converter/charger and then the batteries will still have a "surface charge" left from the charging. So you need to run something like a blower for a few minutes and then check voltage.

A BMS will normally include a current shunt so the meter can adjust its algorithm based on all factors.

typical AGM chart
View attachment 145339

Roger that. Would adding a "Shunt" like the victron help? I'm asking these questions because my wife and I tend to stay on the hook quite a bit and have found that we try not to allow the house batteries to get no lower than 12.4'ish and if they do, we start the generator. I would love a more accurate way to know when it's time to start up the generator if at all possible. My generator has it's own battery for starting.

 

[hughespat57]

A shunt by itself will only provide current amp draw at the moment you look at the ammeter.
When part of a smart battery monitor it records overall energy consumed from the battery to provide a more accurate SOC. "Marine" models like Victron are around $200 and can go up from there.

 

[Blown284]

A shunt by itself will only provide current amp draw at the moment you look at the ammeter.
When part of a smart battery monitor it records overall energy consumed from the battery to provide a more accurate SOC. "Marine" models like Victron are around $200 and can go up from there.

Roger that. I have a Victron 500a smart shunt that I was going to try. I was planning to use it for the house batteries (both of them) wired like they suggest.

 

[dtfeld]

I added Victron Smart Shunts and they are accuarate and a great "fuel guages" for all my batteries. Once wired in, a few setting need to be set via their app and your up and running.

However, if you can still exchange, trade the standard version in for the IP65 version for a few more $$. The leads are potted and the unit much more suited for a boat bilge, you can get the wires/connections up and out of the way. The standard smart shunt works identical, but the connections are open and much more suited to home/commercial solar projects.

The other minor gripe is that the BT range is very limited.

 

[TimzxX]

Hey @Blown284, monitoring your boat's battery voltage is a smart move for peace of mind on the water. While voltage can give you a rough idea of your battery's state of charge, it's not a direct percentage. Typically, a fully charged 12V battery reads around 12.7-13.2V, but it varies with battery type and age.
For a more accurate reading, you might consider investing in a battery monitor like those available at tech-battery solutions. These devices can provide precise information about your battery's state of charge and health, helping you manage your power more effectively during your adventures on the Chesapeake Bay.