Could Dual Wallmount Batteries be Wired More Effectively?

Batteries

Last Post by EG4 Eric 2 weeks ago

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PowerUp

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June 18, 2025 8:18 am

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The QuickStart guides for the 14.3kWh WallMount batteries outline that the second battery should be wired to the first and then the first should be wired to the inverter.

One example is Figure-2 on page 10 of the Indoor WallMount QuickStart Guide.

https://eg4electronics.com/wp-content/uploads/2024/04/EG4%C2%AE-Indoor-280Ah-Battery-Quick-Start-Guide.pdf

Another example is in the 18kPv wiring diagram V1.2 (page 6)

https://eg4electronics.com/wp-content/uploads/2024/09/EG4-18kPV-Battery-Wiring-Diagrams.pdf

However I have seen this similar description and diagram in other EG4 manuals.

Wiring this way will cause the Resistance to be higher for the Second battery (distance from inverter over twice as far) and therefore on a 80% DoD the first Battery commonly will achieve an uneven discharge vs Second battery.

My question: Why doesn't any EG4 manual suggest one of the cables (for instance positive) connect to the second battery instead of the first?

The two batteries would still be connected to each other using the Parallel Cables. With one having the Positive to the inverter and the other battery having the negative to the inverter.

Is there a technical reason, or would there be some side effect / long-term impact I don't recognize?

If my suggestion was a legitimate wiring scenario then the distance to each battery from the inverter would be the same - and enabling them to charge and discharge more evenly.

I have to be missing something as I haven't seen this suggested/discussed in the Forum or offered as an alternative wiring in an EG4 manual.

Appreciate your insights.

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EG4 Eric

June 19, 2025 4:56 pm

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The WallMount batteries have internal bus bars and are designed to be connected to each other as shown in the diagram. This configuration helps keep the batteries balanced and combines their voltages effectively.

If you connect two separate batteries directly to the inverter, each may have a different voltage, which can cause issues. The inverter is only capable of reading voltage from a single battery source, so differing voltages between two batteries can lead to improper operation or errors.

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PowerUp

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June 19, 2025 6:46 pm

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Thank you @eg4eric,

Sorry I could have been clearer. The configuration is 12kPV (only one battery terminal) and 2 indoor wall mount 14.3kW.

I'll include a diagram for my proposed wiring (hoping a picture offers more context). The intention is to use the same Paralleling kit (using the busbars) but wire it so the distance from inverter to each battery is the same.

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EG4 Eric

June 20, 2025 1:28 pm

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Yes, the wiring diagram you provided should work.

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PowerUp

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June 20, 2025 4:50 pm

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EG4 Eric

@eg4eric Thank you, I'll try and post my results.

In my situation the batteries are 10" apart so the 42" conductor can reach the alternate battery from inverter

For the 18kPV or FlexBoss (with Dual terminals at the inverter) do you think we could do something similar? Both negs going to one battery, both Positives going to other battery and parallel connection between batteries?

Of course this would require the two batteries to be close enough together for them to reach.

EG4 Eric

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June 20, 2025 6:29 pm

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PowerUp

@powerup
Yes, that should work as well.

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PowerUp

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June 24, 2025 5:35 am

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SOLVED: I had been utilizing the EG4 recommended wiring for 2 weeks with two new Wall-Mount Batteries. During that time the first (closest battery to inverter) had already racked up an additional cycle (charging and discharging 5% faster) vs the 2nd battery.

From the moment I changed the wiring to equal the distance (diagram above - June19) the batteries have moved in sync with one another. I was able to accomplish this wiring easily because my batteries are only 10" apart (so the positive cable from 12kPv inverter reached to the positive terminal on the second battery.

I have since tested over the last week and cycling 100->20->100 once a day - and both batteries continue to show the same voltage and SOC levels as they charge and discharge.

If you need more details please DM me. I am marking this article as a "solved" (although a complete solution would be for EG4 to document this in their wiring diagrams and mention the possible side-effect of utilizing their default wiring with 2 wall-mount batteries).

Thanks to @eg4eric for checking that my adjusted wiring would not cause irregularities.