Originally Posted by alwier
If you add an extra cell in series to increase voltage, there is no extra increase in actual runtime or aH. Unlike a cell added in parallel. But in parallel, there is no increase in voltage.
Yeah, you don't get more capacity with extra cell in series if you hook it directly up to the bulb. It'll actually consume more current, be brighter and discharge the entire pack faster. However, if you use a switching-regulator with very minor loss, it will output a steady 12v output even when the battery's at 14.8v. This runs the bulb at a lower amperage than if you hooked up the battery directly. You'll get a longer run-time before the battery discharged to 12v. It flattens out the sloping discharge-curve and makes it wider; gives you longer run-time until a certain discharged level.