Even though the batteries perform the identical job of delivering high-rates of current to crank internal combustion engines, the “use model” of batteries employed in gensets is different in one key respect from those employed in vehicles. Batteries used on gensets are charged around the clock, whereas vehicle batteries are charged only intermittently.

Flooded SLI batteries used in genset applications fail sooner and more suddenly than vehicle applications because of a series of very logical assumptions, one of which is incorrect.

In vehicle applications the different materials composing batteries tend to fail in a gradual manner at about the same time. This graceful failure mode is not an accident. Battery manufacturers have had decades to optimize SLI battery designs such that batteries used in vehicles enjoy a reasonable battery lifespan. All non-value adding cost is eliminated from the battery such that all components of the battery have approximately the same longevity under normal use conditions. The battery works very well in the application for which it was designed. The fact that the same batteries don’t last as long in genset applications suggests that the difference in use models between gensets and vehicles likely accounts for the difference in battery longevity and suddenness of failure.

One of the basic assumptions made by SLI battery designers is that batteries are charged intermittently. The assumption is logical and reasonable because the majority of vehicles are shut down a large part of each day -- no charging is taking place. Batteries in gensets, however, are on charge around the clock. As we will see, the number of hours a battery is on charge is very relevant to both SLI battery life and the actual failure mechanism.

Gensets employ a battery charging strategy that is very different from vehicle charging. Mandated by the National Electric Code, the National Fire Protection Association and Underwriters Laboratories, emergency and standby gensets employ static battery chargers that continuously “float” charge the battery. The purpose of this is twofold: to insure that that battery is fully charged at all times, and to power accessory equipment connected to the DC bus such as electrical switchgear and supervisory systems necessary for the generator system to function.

The flaw is that telecom and switchgear batteries are purpose-built to be continuously float charged. SLI batteries, however, are not designed to be float charged, and suffer premature failure when they are.

The tacit assumptions behind mandating continuous float charging for gensets are as follows:

- Emergency generators are a critical application.

- Float charging is successfully employed in other critical applications such as telecommunications and electrical- switchgear.

- Therefore continuous float charging should be employed with genset starting batteries.

Although in hindsight these assumptions seem logical, there is a flaw. The flaw is that telecom and switchgear batteries are purpose-built to be continuously float charged. In contrast, starting batteries are purpose-built only to be intermittently charged. Here is why continuous float charging of flooded SLI batteries is a problem.

****This article is collected from https://sens-usa.com/.

Conclusion:

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