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With a 12V AGM battery bank of 3 or more batteries wired in parallel, is charge able to be drawn by attaching to any random positive and negative terminal across the battery bank?

Is it optimal to draw charge by attaching to the positive and negative terminals that are furthest apart?

If so, what is the advantage?

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  • \$\begingroup\$ Connecting 12V AGM batteries directly in parallel can be very dangerous if you don't know what you are doing, and it sounds like you don't have much experience with this. I suggest that you don't even try this. \$\endgroup\$ – Elliot Alderson Feb 12 at 13:20
  • \$\begingroup\$ @ElliotAlderson I’ve connected and used 2 x 130Ah AGM batteries in parallel many times before without any issue. I simply connected positive to positive and negative to negative with short heavy duty copper wire and used the positive terminal on one battery and the negative terminal on the other for output. I want to repeat this connection by adding a third battery to the bank and use best practice in terms of selection of positive and negative terminal to use for output. What kind of danger are you pointing at? \$\endgroup\$ – Guru Josh Feb 12 at 17:48
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    \$\begingroup\$ See the answers posted for this question: electronics.stackexchange.com/questions/393085/… \$\endgroup\$ – Elliot Alderson Feb 12 at 23:17
  • \$\begingroup\$ @ElliotAlderson I always use an 80A fuse attached to the positive terminal that I use for output. \$\endgroup\$ – Guru Josh Feb 12 at 23:22
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    \$\begingroup\$ No, you need a fuse on each of the batteries for fault protection. See also cdtechno.com/pdf/ref/41_7952_0112.pdf \$\endgroup\$ – Elliot Alderson Feb 12 at 23:59
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When the wires behave as wires, then you can use any random positive and negative for the outputs. When the wires behave as resistors, then you need to think.

What's the difference between a wire being a wire, and being a resistor? It's the current being drawn, and the voltage drop that that creates across the wire.

For a few mV or even 10s of mV (for instance 10A through 1m of 10mm2 wire gives 17mV drop), then use any random terminals.

If you have a significantly higher drop, then you should connect all your cells by equal lengths of cable to a star point, so that the load is shared equally between the batteries, and that one doesn't handle the lion's share.

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