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I recently replaced the battery in my APC Back-UPS CS 650 and of course I didn't opt for an original APC battery, but just bought a similar one from the corner electronics shop.

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Apart from the label both batteries looked exactly the same, but still the old one used to provide 20 minutes of backup time and the new one only 10 minutes. The label on the original battery only states 'original APC replacement' and things like 'wash your hands when spoiling the acid contained in it'. Nothing indicated exact specs, so I just bought one that looks exactly the same and has similar voltage (12V).

So what is different, does APC really manage to put 14Ah in their original battery and still only have a 12V/7Ah form factor? Did I buy a bad battery? Is it a difference between deep cycle vs. non-deep cycle battery? Are there different types of batteries that I should have been aware of before buying one?

replacement battery 12V 7Ah

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According to APC, the original RBC17 battery has "108 Volt-Amp-Hour" (i.e., 9 AH) capacity.

It may also have better deep-discharge characteristics than a generic 7AH battery.

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  • \$\begingroup\$ Interesting find, it is exact same dimensions as the 7Ah battery I have now. 12V/9Ah are quite a bit harder to find, but indeed they exist (according to Google). \$\endgroup\$ – jippie Sep 26 '12 at 6:58
  • \$\begingroup\$ 9Ah batteries share the same dimensions as a 7Ah one, but weigh slightly more. They may have additional lead plates over the 7Ah ones, or may be designed with a pattern giving more surface area to the plates. Either way they have more Lead and/or Acid inside to provide more capacity. As such the 9Ah battery costs ~20% more too. \$\endgroup\$ – Criggie Jul 28 '17 at 10:58
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For normal UPS use any old battery will do for typical use cases where the UPS infrequently provides power for long enough to safely shut-down the computer etc.

If you are using the UPS as a long term usable power source, then you should get batteries designed for UPS work

You can replace the battery with a much larger one, but you then need to make a new housing for it, or at least fully insulate the external leads. It will take longer to re-charge, but will otherwise work as normal, and give you a much longer UPS operation. I once added a large deep-cycle battery to a standard 750W UPS to give it 24 hour server operation!

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  • \$\begingroup\$ Downside of doing this is that the inverter may not be rated to invert continuously for 24 hours - it may have an active service window of ~2 hours. If your donor UPS had options for external battery packs, then that's a good sign the inverter is up to the task. Fires are bad for uptime, `mkay. \$\endgroup\$ – Criggie Jul 28 '17 at 10:55

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