8. What's a gel-cell battery?
The gel cell is also an AGM, but with silica gel added to the electrolyte, which gives it the consistency of Vaseline. Gel-cell batteries typically have a lower self-discharge rate than other AGMs, and are used in applications where there are a lot of parasitic electrical demands on the battery-such as from a clock, or a radio with station presets-when the engine isn't running. As of this writing BMW is planning to equip some of its new models with gel-cell batteries. To charge its gel-cell batteries, BMW recommends using its own special charger-built for BMW by Deltran, which has a peak voltage slightly lower than that of typical battery chargers. But the difference in peak voltage and charge timing between it and chargers such as Deltran's Battery Tender and Yuasa's SmartShot may be so slight as to have no practical effect on the battery's life. With so few gel cells currently in the field, the jury is still out. But in the meantime, if you have a BMW with a gel-cell battery, use the BMW-approved charger, if only for your warranty's sake.