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I have a APC UPS with a 9 Ah battery.

Would it be ok to replace it with an 18 Ah battery?

I realize that some modifications would be needed since it won't fit in the case.

fixit7
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In theory it shouldn't matter how much bigger the Ah rating of the battery is as long as you regulate the Current and voltage the same. It just takes long to transfer the coulombs of charge. A bigger battery of the same chemistry will have a larger capacitance and may have a lower ESR.

Tony Stewart EE75
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  • I added the new larger battery. It's at 83%. Any suggestions on what to use the old one for? – fixit7 Jan 22 '18 at 21:08
  • I have the same question, have a APC Back-UPS Pro 550 that needs an expensive RBC110 battery with 8400 mAh at 60 euro. I can get alternative 12V deep cycle batteries with 13Ah or more for a lower price! It would not fit inside the case but that doesn't matter, I can even put a tray under it in case it ever boils over in a worst case scenario. @TonyStewart The voltage is the same but do you have any suggestion on how to regulate the current? Wouldn't the UPS already do that automatically? – Louis Somers May 08 '20 at 22:19
  • fixit 83% of what? @LouisSomers yes deep cells should use similar profiles and are temperature dependent for cutoff and float voltage .There is also a wide range in prices https://www.google.com/search?q=BE550G,+BE550R&client=firefox-b-d&sxsrf=ALeKk00lmksfR0kI2Z0PueNtAVG493A4fQ:1589041567206&source=lnms&tbm=shop&sa=X&ved=2ahUKEwj61JWRmafpAhWbAZ0JHRkuCfYQ_AUoAXoECDQQAw&biw=1575&bih=960 – Tony Stewart EE75 May 09 '20 at 16:28