In my recent threads wrt Greenworks 60v batteries, I think the following comment's by flippy is applicable:
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Re: Greenworks 60v rebuild
by flippy » Mar 06 2019 2:11am
sorry, but that is very dangergous idea, especially for commercial usage.
having 2~3 packs in a product and one dies for whatever reason means the load gets transferd to the other packs wich means those will also conk out.
commercial use means it will keep being used as long as its works so you can be down to one pack and they will still hammer it.
a recepy for disaster and very expensive repairs.
in commercial uses it MUST shut down otherwise it will be run into the ground.
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Or as fetcher was saying: "Generally it's better to use one big battery as opposed to several smaller ones used one at a time. This reduces the strain on the cells and they will live longer. Combining multiple smaller ones in parallel works but you have to use diodes or have some way to prevent connecting packs of significantly differing voltage."
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So what flippy and others are advising is that running parallel packs isn't recommended. OTOH I am actually doing the same kind of project as you, 60v 4aH batteries to run a Bafang with a DROK buck converter to protect the Bafang electronics. Lately I inclining toward the 58v Echos because I can eliminate the DROK since Bafang computer has an over-voltage threshold of 61.5v but not more. Another thing I like about the Echo 58v batteries is the thicker rail guides which makes fabrication easier. Greenworks has slimmer rail guides but DIY rack mounts are not very difficult for either brand.
Personally I am going to follow their advice and install battery isolation switches, cheapest off the shelf option for me is the ones used on RVs and boats to manage dual batteries. For three batteries, that would be a second isolation switch since it's difficult to find switches for a triple set of batteries. A single-pole, triple-throw switches(SP3T) are expensive so it's cheaper to just get two of the dual battery isolator switches.