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Do I really need to charge both EG4 Wallmount Batteries to 100% before connecting in parallel to 6000XP?

fn.humboldt

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Sep 5, 2024
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Whitethorn, CA
Section 3.1 of the Connection Overview & Paralleling Guide for EG4 Wallmount Batteries says:

When installing multiple batteries or adding a batteriy to an existing rack, please ensure that all batteries are charged to 100% before paralleling together.

I just bought a second EG4 Wallmount battery to add to an existing 6000XP plus Wallmount battery. Is it really necessary to charge both to 100% or will the BMS figure it out?

I’m not sure how I’d get them both to 100% other than connecting my generator to each battery individually to top them off.
 

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Ideally both batteries would be charged to 100% before connecting in parallel, this practice will eliminate lots of potential balance problems. That said, the important factor is that the voltage of both batteries is the same, Plus or Minus 0.2V, so you don't get major sparks and high initial flow of current from one battery to the other.

Since the Voltage vs. State of Charge of LFP batteries is rather flat across a large portion of its usable power curve, equal voltage does not guarantee equal SoC. So if the voltage is close enough and the batteries are connected together then they should both be charged to 100% and allowed to float at the manufacturers recommended constant voltage until the BMS in both batteries shows all the cells to be balanced.
 
Just get the voltage close as @BentleyJ says to prevent large currents, and then fully charge them and let them spend enough time fully charged to be internally balanced
 
All manufacturers put useless, unnecessary steps in their manuals to make your life more difficult. I'm sure there are lots of other steps in the manual you can ignore and maybe nothing bad will happen.
 
Get the voltage reasonably close, make sure the breaker is off on the new one and connect to the existing and then flip the breaker.
They will level out and sort it all out, after a few cycles they should track pretty close to each other.
 

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