Hello, I am using a 7AH 12v lead acid sealed to run a USB/ 5v fan (normally runs on 2X 18650 batteries or USB), through a car USB adapter. Fully charged battery reads 13v. After running the fan 2.5 hours I notice that the fan has slowed down. So I disconnect and check the battery. It reads around 6.5v. Disconnected battery. After leaving it overnight without charging, it reads 12.6. I connect the fan again. Run it for 4 hours. Battery reads 6v. After just 30 minutes, it reads 9.8. I am waiting to see what the final recovery number will be. Is this behavior normal or is something wrong with battery? It is an old used battery.

If I were using a battery low voltage controller that shuts the system down at say 10v, the fan would have shut down long time ago. Or will it go off and on, off and on as it drops to 10v and then recovers etc. Should I use such a controller? Thanks.

  • Leon replied to this.

    Hello unn

    I think your battery is dead, have you think about lithium batt replacement ? LFP is cool

    Maybe a lead acid battery will answer you better than me I am not really lead acid specialist sorry

      UPDATE: After about 6 hours the battery recovered back to 12.2v.

      Leon: thank you. Yes, the fan has 2X18650 in parallel which lasts about 2.5 hours. I was just hoping that 7AH battery will last longer, which it does as I reported in original post but with a draw down in the voltage.

      12 days later

      Try lithium-ion battery, it is better than lead acid battery.

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