Hi Randall, Through long experience I have found that only the original Lead Acid AGM or Gel Cells that come in a brand new UPS have anywhere close to 5 years in them. Any time I have replaced a set of these in a UPS no matter how much money I have spent on whatever kind of batteries I've never gotten 5 years again. At most it's been 3 years. Sometimes 2 years. Maybe the Lithium batteries are going to be better but those UPSes are too spendy for my budget, yet.
Now, the "textbook" answer from APC is that their SmartUPSes have a "calibration mode" The way this works is, you put a set of fresh batteries in an SmartUPS. Then you let them completely charge for a day or so. Then you run a calibration test from the control panel of the UPS. The test puts the batteries under load and starts a clock and then starts checking the voltage of the batteries. When the battery voltage drops below 11.2 volts or some such then the test stops. The UPS then "learns" the battery's "discharge curve" and changes a calibration factor. The factor allows the UPS to tell how long the battery is going to last when put under load. The SmartUPS then weekly self-tests the batteries by putting them under load for a few seconds. Based on what level the battery voltage drops as a result of being put under load the UPS is then supposed to be able to predict how long the batteries are going to last in a real blackout. When the batteries are a year old then you are supposed to run a calibration test again which figures out if the calibration factor needs to be changed. Now, I do not know if this testing by APC is really able to predict how long an actual battery lasts or whether it's snake oil. The articles I have read on lead acid batteries all seem to say some basics. First point is that if the battery is overcharged then the electrolyte starts boiling off the water. (ie: converting the water into free hydrogen and oxygen) With a car starting battery this is not a problem since if you just check the electrolyte level and keep the battery topped off, then you are fine. With a sealed lead acid battery then the electrolyte paste has some magic chemical in it that supposedly "recombines the hydrogen and oxygen back into water" The second point is that temperature matters greatly. Here is the output of apcupsd from my 14 year old SmartUPS: root@officeserver:/usr/home/tedm # apcaccess APC : 001,042,1055 DATE : 2026-06-10 22:29:42 -0700 HOSTNAME : officeserver VERSION : 3.14.14 (31 May 2016) freebsd UPSNAME : APCUPS CABLE : USB Cable DRIVER : MODBUS UPS Driver UPSMODE : Stand Alone STARTTIME: 2025-12-17 05:22:44 -0800 MODEL : Smart-UPS 1500 STATUS : ONLINE LINEV : 120.9 Volts LOADPCT : 29.2 Percent LOADAPNT : 22.7 Percent BCHARGE : 100.0 Percent TIMELEFT : 56.0 Minutes MBATTCHG : 5 Percent MINTIMEL : 3 Minutes MAXTIME : 0 Seconds OUTPUTV : 120.2 Volts DWAKE : 0 Seconds DSHUTD : 0 Seconds ITEMP : 27.0 C BATTV : 27.2 Volts LINEFREQ : 60.0 Hz OUTCURNT : 2.75 Amps LASTXFER : Automatic or explicit self test NUMXFERS : 7 XONBATT : 2026-06-03 07:45:32 -0700 TONBATT : 0 Seconds CUMONBATT: 46 Seconds XOFFBATT : 2026-06-03 07:45:41 -0700 LASTSTEST: 2026-06-03 07:45:33 -0700 SELFTEST : OK STATFLAG : 0x05000008 MANDATE : 2012-11-03 SERIALNO : AS1244115771 BATTDATE : 2023-12-14 NOMOUTV : 120 Volts NOMPOWER : 1000 Watts NOMAPNT : 1440 VA FIRMWARE : UPS 15.0 / 00.5 END APC : 2026-06-10 22:30:23 -0700 root@officeserver:/usr/home/tedm # You will notice that there is an internal temp there. This is because this model of UPS has an internal temperature sensor. You will also notice that 27C is at the top upper limit of ideal operating temperature. This model of UPS has 100% steel case and this particular UPS is sitting on the concrete floor of my basement so it's as cold as it can get yet there's still heat in the UPS. You will also note that the battery date is 2023. This is because when I last changed the batteries in this UPS I configured that date into the NVRAM of the UPS. You will note the load % is about 30%. This is around the minimum amount of load needed for an adequate self-test. Too little load and the UPS will not be able to drain the batteries at all during a 3 second self-test and thus will not be able to get usable data regarding the battery. You will also note "timeleft" is 56 minutes. ] I think that it is probably not possible for a 3 year old sealed lead acid battery set to power a 2.75 amp load plus the inverter power loss for an hour. The ridiculous timeleft, the excessive heat, really point to the beginnings of thermal runaway. These batteries are close to the end of their life - even though the UPS self test has NOT caught this yet. They now have significant internal resistance and are generating excessive heat in the UPS I should replace them. Ted -----Original Message----- From: PLUG <[email protected]> On Behalf Of American Citizen Sent: Wednesday, June 10, 2026 5:37 PM To: [email protected] Subject: [PLUG] hammered by sudden UPS power failure during a key backup To all I am struggling to recover from a very bad power failure during a key upgrade from my OS openSuse Leap 15.6 to Leap 16.0 upgrade. My UPS unit completely clicked off right during the backup. It has been several hours now and I am trying to carefully pick up all the pieces and verify that I did NOT lose any data. My question to all of you is simple: How can you tell the health of the lead-acid batteries in your UPS unit? >From what I can gather, this cannot be done live via any linux operations. My lead acid batteries were shot, and bulging out their case. Yes I was aware that I had 5 years time on these back up lead-acid batteries and was risking total failure, which actually occurred this afternoon for me. How do you keep on top of the UPS units so you don't have a rather foolish incident like mine today? Randall p.s My unit was the Cyberpower CP1350AVRLCD (see https://www.cyberpowersystems.com/product/ups/intelligent-lcd/cp1350avrlcd/)
