ASK THE EXPERTS: Battery Charging Rates

Surrette Battery Bank
Is there a standard maximum charge rate for flooded lead acid batteries?
Surrette Battery Bank

Is there some sort of a standard maximum charge rate for flooded lead acid batteries? Someone mentioned not wanting to take them beyond a C/10. What’s the rationale for that? I’d rather hit them hard and fill them up quickly while my generator is running. Thanks,

John Bartlett • Exeter, New Hampshire


Hello, John. The maximum recommended rate is C/5 (a charge rate in amps of one-fifth the overall battery capacity in amp-hours), but only when the cells are between 10 and 85 percent state of charge (SOC). After the cells reach 85 percent SOC, then a C/10 is the maximum. After cells reach 95 percent SOC, between C/20 and C/15 is recommended. Having said this, I rarely charge faster than a C/10.

The reason for the maximums is heat. Higher amperage means more heat, particularly when the cells are getting fully recharged. Thermal cycling wears the plates and sloughs off material.

Finally, it’s always a good idea to get charging specifications from the manufacturer of the particular model of battery you’re running. Battery specific charge rates, and bulk, absorption, float and equalization set-points and times will all lead to better battery longevity.

Richard PerezHome Power

Comments (2)

Justine Sanchez's picture

Thanks for posting your comment/question! So when you wire batteries in series you are increasing your voltage, but the amp-hrs and thus the charging amps remain the same. For example, say you had two 12V, 25Ah batteries wired in series, this makes the voltage 24V, but the amp-hrs remain 25Ah for the battery "string". Thus the charge current, if we assume the max of C/5, would remain 5A (25Ah/5hr). So you keep the same charge current, but the charging voltage needs to double.
-Justine Sanchez
Home Power Magazine

prasidhda's picture

Suppose A certain battery has charging current of 5A. And if we connect same battery in series with earlier,what will be the charging current?is it remain same,gets double or halved?

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