[see Forum Thread
this is taken from for more]
Wiring Batteries in Parallel
Here's a current representation of 4 batteries with the same internal resistance in parallel being charged with a 50 amp charger.
Notice anything wrong?
In order for the batteries to age at the same rate, they should be charged
at the same rate. It's not to uncommon to see configurations like:
This is better, but still not ideal. How they're arranged to get the perfect balance is all about resistance
. This is why you hear folks saying the cables should be the same gauge, the same length, etc.
Don't worry too much if that matches your existing configuration, the numbers in the illustration are using a thin guage and are a bit exaggerated to illustrate a point.
Gauge 0 wire has a resistance of about 100u/ft and new lead acid batteries have an internal resistance of around 50 millOhms going up to an ohm as they age. It's easy to build a circuit with tools like https://www.falstad.com/circuit/circuitjs.html
. You can import the attached file Parallel1.txt into the program and play with the circuit to adjust things. In the circuit, batteries are represented in columns as a "voltage source" and "internal resistance". On the far right is a 2nd battery at a higher voltage acting as a charger. Horizontally are "resistors" representing the wires interconnecting the batteries.
Now that you've done your analysis and figured out the optimum cabling, did it look like this: