I'm considering using a 4V 1Ah lead acid battery to power my embedded system project. I want to charge this battery at its float charge voltage. Does the current have any significance at the float charge point? For example, would charging this battery at 500mA at float charge voltage damage it?


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For example, would charging this battery at 500mA at float charge voltage damage it?

You cannot charge a battery, or supply anything, with a fixed voltage and current. You fix one, the load fixes the other.

A discharged battery of that size, if connected to the float voltage, will probably try to draw several amps. If your power supply current safely limits at 500 mA, then its output voltage will drop. That's you setting the current, the battery sets the voltage.

Once the battery is more fully charged, it will draw less current than 500 mA, and the voltage will rise to the float voltage. Then you've set the voltage, the battery is setting the current.

If it's a sealed, oxygen-recombination, battery, then at the float voltage, the charge current should eventually drop to low enough that the internal chemistry recombines the oxygen and hydrogen released during charging. IIRC, that's typically below the C/100 to C/200 ballpark, the battery data sheet should tell you.

If the current hasn't dropped to that low value when the battery is fully charged, then you may have a faulty battery, or be supplying it with higher than its float voltage. Continuous charging at too high a current will overload the oxygen combination route, and you'll irreversibly damage the battery.

A vented wet cell should drop to a similar low value of current when floating, but here you will steadily lose water due to the passage of current, and the battery will require topping up from time to time.

  • \$\begingroup\$ I was wrong about a lot of things. You really enlightened me. Thank you so much! \$\endgroup\$
    – A. Vehbi
    Commented Feb 10 at 8:53

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