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rockies
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# Posted: 24 Oct 2018 20:41 - Edited by: rockies
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I was reading in an article that you should never use volts to determine the State of Charge (SOC). It is extremely inaccurate and difficult if you want to do it right.
It said to know the state of charge on your batteries you should use a battery monitor like this.
https://www.victronenergy.com/battery-monitors/bmv-700
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Mike 870
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# Posted: 24 Oct 2018 21:20
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I just bought the BMV 712, I'll let you know what I think of it once I get it up and running. I also bought a hydrometer, So I should be able to tell if it's reading fairly accurately.
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Wilbour
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# Posted: 24 Oct 2018 21:52
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But it shows the state in volts....
Or does it use the current drain and then estimate the volts?
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creeky
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# Posted: 24 Oct 2018 22:00
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Quoting: Wilbour use the current drain and then estimate the volts
Pretty much. You "syncronize" the bmv when your battery is at 100% charge a couple of times and then it keeps track of the charge level.
Of course with lithium batteries lack of resistance you can use the voltage as a battery state of charge indicator without indicator.
The BMV also lets you measure mid-point voltage. This divides your pack in half and measures both. Useful with either lead acid or lithium for tracking "balance."
It can give you an early warning if you have a cell going bad.
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Nate R
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# Posted: 25 Oct 2018 08:37
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Before I'd seen this Victron, I bought the Trimetric 2030, which also monitors battery in/out. Been happy with it, great for tracking daily usage and charge.
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creeky
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# Posted: 25 Oct 2018 10:07
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Good point Nate. THere are other battery monitors. There are also really inexpensive ones from China. They don't have bluetooth etc. But for 20 bucks...
I've used them many times. Some even have relays that will control things ...
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Wilbour
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# Posted: 25 Oct 2018 16:00
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Golly, those items are not cheap!
Victron looks way nicer but since I bought the bluetooth dongle for my Victron already it offers me more flexibility.
Man, I love my supplier (in a customer/retailer kinda way) 
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ILFE
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# Posted: 26 Oct 2018 05:52
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rockies, in my opinion, a hydrometer is probably the best way to check the state of charge of a flooded lead-acid battery.
Aside from that, my vote would be for a battery monitor as well.
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