Originally Posted by Ljswany
My Renogy has a 15 foot cord. My question is this: Would the batteries charge slower if the wires are longer? I know wire gauge can have an effect on this as well.
Yes, with a longer cord the batteries will charge slower. And yes, wire gauge has a significant impact.
I took the liberty of guessing your current gauge size and guessing the amperage of your portable panel, and did some on-line calculations.
You can conclude from these numbers that doubling the cord length would require that you increase (smaller numbers) by 2 sizes in order to maintain the same charge. 2 sizes (standard American sizes) means for example from 18 ga up to 14 ga.
Actual panel amperage doesn't actually matter. All that matters is that if you double the wire length you need to go up 2 sizes from what you start with.
There is in fact a tiny, insignificant, bit of improvement if you read the voltage drop numbers. Use this smidgen of improvement to your advantage by leaving a couple of feet of the original thinner wire attached to the panel and connect the 30 feet of new wire to the smaller wire for a total of 32 feet.
The real downside to going up 2 sizes is going up in price by 4 times. Ouch!
PS. I just noticed I used AC current instead of DC current. It makes no difference at all for calculating voltage drop in this application.