![]() Sealed lead-acid (SLA) and gel batteries are particularly sensitive to overcharging, since any lost water cannot be replaced. Furthermore, since the electrolyte level has dropped, a portion of the plates are now exposed to air, causing plate oxidation and reducing battery capacity. The concentration of the sulfuric acid in the electrolyte increases, which is damaging to the battery plates and reduces battery life. Overcharging lead-acid batteries causes the electrolyte water to break into oxygen and hydrogen gas, which depletes electrolyte levels in the batteries. Both the overcharging and undercharging of lead-acid batteries will cause battery life degradation.įigure 1: Top of stack voltage is not divided evenly across the batteries in the stack Since not all batteries in the stack will share the charge evenly, some of the batteries in the stack might be severely overcharged while one or more of the other batteries in the stack may remain undercharged. Figure 1 depicts a scenario in which the top of the stack voltage is programmed to be 53.2V, but the individual battery voltages are unknown and may not all be 13.6V. In most series-connected battery stacks, only the voltage at the top of the stack is measured, and it is assumed the batteries in the stack are matched and hence share charge equally. This problem is true for all battery stacks made with batteries of any chemistry, not just lead-acid batteries. Replacing a failed battery itself does not solve the problem, since the replacement battery’s characteristics will be very different from the other batteries in the stack, and stack failure would recur. At that point, the entire battery stack is deemed to be bad, and all the batteries in the stack require replacement. Batteries connected in series will drift over time due to unequal leakage currents, and capacities of individual batteries may change over time.Įxtreme operating conditions and frequent discharge cycles further exacerbate these problems, which eventually cause one of the batteries in the stack to fail. There are variations in battery specifications due to limitations in the manufacturing process, and when multiple batteries are stacked in series these specifications no longer apply to the battery stack. Furthermore, these specifications only apply to a single battery. When batteries are manufactured, they must conform to tight specifications for parameters such as energy capacity, ESR (effective series resistance), leakage current, and the number of discharge cycles before failure to ensure quality, guarantee a minimum lifetime, and meet various standards. When a single lead-acid battery in the stack fails, all the lead-acid batteries in the series stack need to be replaced to maintain battery stack performance. In all the examples, two or more lead-acid batteries are connected in series. Golf carts and other industrial electric vehicles are typically powered by a stack of series-connected lead-acid batteries. Series-connected lead-acid batteries find extensive use in the UPS (uninterruptible power supply) industry to provide backup power when the mains power is lost. Energy storage solutions (ESS) use lead-acid batteries in a variety of series and parallel configurations to store energy generated by renewable sources such as wind and solar. ![]() The telecom industry uses a series stack of four lead-acid batteries to provide a 48V stack. Lead-acid batteries are widely used in a broad range of industries and applications.
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