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I've been working on a small project to add electrical to my utility trailer. I have two 12V 20Ah lead acid batteries wired in parallel for running a mix of lights, a winch, cameras, a ventilation fan, inverter, etc. (Basically more of a fun, learning project). The specific batteries are:

battery

https://www.amazon.com/gp/product/B00KC39BE6

Originally I was going to keep them separate and divvy up the electrical devices between them, so I purchased a battery meter for each one:

battery meter

https://www.amazon.com/gp/product/B01N642QV6

I've since learned about and changed over to wiring them in parallel connected to a single charger, but now I'm wondering if there is an arrangement where I can still use the meters to read each individual battery without reading the output of the overall bank?

I tried to Google this, but I get the feeling that if this is feasible, I don't know the correct terms to search for.

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  • \$\begingroup\$ I'm not familiar with multi-cell lead acid batteries, but I can tell you that measuring and balancing individual cells in a lipo battery pack is very common, and multi-cell batteries are typically built with wiring harnesses that are designed to allow this. Google search "lipo battery balancing" or "lipo balance charger" to get some ideas of typical approaches. I'm assuming there's an equivalent for lead acid that follows the same general approach. \$\endgroup\$ – dwizum Aug 15 at 20:08
  • \$\begingroup\$ @dwizum Only if they're in series, not parallel. \$\endgroup\$ – DKNguyen Aug 15 at 20:45
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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. The proposed circuit.

Once you wire the batteries in parallel you will have the circuit of Figure 1. Red is positive and black is negative.

It should be fairly clear that all points on the red line will be at the same voltage (assuming you use a large enough cable cross-section) and similarly all the black line will be at the same potential. Your two meters will therefore show the same voltage reading.

You can't use them to measure current as they have only two wires and will require something in the region of 9 to 16 V to operate the meter and backlight.

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  • \$\begingroup\$ Thanks for the clear informative answer. That's what I was expecting but decided to ask a more knowledgeable group to confirm. I'll just go with one meter to measure the overall battery bank. (And of course I already cut holes in my control panel for both meters, so I'll have to figure out something to do with the extra hole.) \$\endgroup\$ – TomTheCoder Aug 16 at 2:42
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I don't think it is possible. In parallel everything has the same voltage potential. As you mentioned you can measure the output of the combined cells.

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  • \$\begingroup\$ You could with current balancing resistors, but those are kind of counterproductive if all you want to do is use them to monitor batteries. \$\endgroup\$ – DKNguyen Aug 15 at 20:46
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I'm not sure you can, because you are forcing the same voltage in both batteries by connecting in parallel.

What you could measure is the current, that will vary with the charge of each battery, but I'm afraid that your meter is only for voltage.

I hope to have helped you!

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