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I encountered the following issue: the lead-acid batteries (2 * 12V 7Ah) that power up the stair lift motor (24V, 0.3 kW) died (the motor wouldn't start anymore, with a nominal voltage at no load of about 12.0V or less for each battery; didn't check them at load) after just 1 month of usage. The lift was lightly used, at most 6 times a day, with a ride of only 6 steps.

The previous batteries lasted for one entire year.

I checked the charger (24V, 300mA switched mode power supply) and is suplying succesfully 24.6V when the lift is at the end of the rail. The new batteries are charged full time with 24.6V and 0.04A (which means that the batteries are full from what I can remember.. 3% of 7Ah is 0.21 Ah).

  • should I change the power supply with a less nominal current given the fact that the batteries are full time on-charge?
  • should I disconnect the power supply from time to time so that the batteries won't charge continously?
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  • \$\begingroup\$ What was the quality of the replacement batteries compared to the original? \$\endgroup\$
    – Solar Mike
    May 13 '21 at 10:16
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    \$\begingroup\$ 24.6/2=12.3 V per battery. That’s way too low and no wonder the battery died. \$\endgroup\$
    – winny
    May 13 '21 at 11:26
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    \$\begingroup\$ If they were normal "wet" or AGM Lead-Acid batteries, they should have been charged to at least 13.8V per battery, 27.6V in total. I.e. they were never properly charged. \$\endgroup\$
    – StarCat
    May 13 '21 at 11:38
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    \$\begingroup\$ 100% agree --- 24V is not adequate to charge 2 12V lead acid batteries. That said, note it's possible often to renew slightly abused lead-acid batteries by doing a 'wake up' on them. You have not hyper-abused these (yet). A wake-up is simply fully discharging, then fully charging them about FIVE times. In other words... I recommend you get a proper 24V charger and hook it up before buying new batteries. Charge them up, then disconnect it and ride the lift until they die... repeat 4x more times. \$\endgroup\$
    – Kyle B
    May 13 '21 at 13:49
  • \$\begingroup\$ Thank you all for your answers! \$\endgroup\$
    – tibi10
    Jun 17 '21 at 15:06
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The long term "float voltage" is 27.1V for a flooded lead acid battery (at room temperature).
When recharging, it is common to pull them up to above 28V until the current drops below some threshold and then go down to 27.1.
Not an ad for them but this can help:
https://www.power-sonic.com/blog/how-to-charge-a-lead-acid-battery/

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