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I have a UPS, its battery seem to be dying. Earlier it was giving a backup of 30 min, now it has come down to 10 min with the same load. I purchased a battery of the same capacity 12V 7amp, I was thinking of connecting this one with a 2-way switch, so I can use both batteries by switching it when one gets discharged. Is this a right thing to do, will it create a problem?

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You can't switch your battery under load, that would lead to an inevitable voltage drop on the generated voltage keeping your devices working, and thus negate the idea of a UPS.

So, give your old battery into recycling, and only use the new one – even using both in parallel (if that was possible, which is not really the case) would be giving you but 25% more capacity than just the new one, so simply write off the old battery.

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  • \$\begingroup\$ How does adding a second battery in parallel only add 25% capacity? \$\endgroup\$
    – JYelton
    Commented Jun 1, 2020 at 15:27
  • \$\begingroup\$ And the UPS won't be designed to charge two batteries. \$\endgroup\$
    – Transistor
    Commented Jun 1, 2020 at 15:27
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    \$\begingroup\$ @JYelton, the 25% (or so) is from the original battery. \$\endgroup\$
    – Transistor
    Commented Jun 1, 2020 at 15:28
  • \$\begingroup\$ Putting aside UPS capabilities for now (I recognize they aren't designed to charge nor house extra batteries), adding an identical battery in parallel should maintain voltage while doubling capacity. Is the 25% figure due to the failing battery? I just am curious how 25% was arrived at. \$\endgroup\$
    – JYelton
    Commented Jun 1, 2020 at 15:31
  • \$\begingroup\$ @JYelton you already got an answer to that question from Transistor. \$\endgroup\$ Commented Jun 1, 2020 at 15:38

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