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I have two batteries 12V GEL 130Ah, each charged to 14.4V. After connecting them together in parallel, the voltage drops gradually and equalizes at 12.99V. (I use 10mm^2 short cables to connect them together so I wouldnt expect much of a drop at the cable.)

I would expect voltage to stay the same. Why does the voltage drop occur? Does it mean that the battery bank is somehow faulty?

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  • \$\begingroup\$ And if you don't connect them in parallel does the voltage fall to 13 V as well? \$\endgroup\$ – Transistor Aug 4 '18 at 19:29
  • \$\begingroup\$ No, no load is connected so it stays at 14.4V \$\endgroup\$ – Adam Wolski Aug 4 '18 at 19:36
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    \$\begingroup\$ 14.4V is the maximum charging voltage. It's really hard for me to believe that if the batteries set for awhile, disconnected from the charger, that the voltage is still 14.4V. Is that what you are saying? \$\endgroup\$ – Elliot Alderson Aug 4 '18 at 20:29
  • \$\begingroup\$ @ElliotAlderson Batteries set off the charger for ~30sec, no load applied in the meantime \$\endgroup\$ – Adam Wolski Aug 4 '18 at 22:30
  • \$\begingroup\$ So the scenario is this: the batteries are fully charged and then connected together in parallel, and as soon as it happens the voltage starts dropping... \$\endgroup\$ – Adam Wolski Aug 4 '18 at 22:31

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