This isn't the right way to look at it.HoseCrusher wrote:Keep in mind that in order to get to around 12 volts you need to use 3 of those cells.
Now you have a battery pack of 3 cells with a nominal voltage of 3.7 * 3 = 11.1 volts and a capacity of 42 Ah.
How does that compare to a 12 volt lead acid battery?
I couldn't find any info on the cell organization of this pack. Since lithium packs almost always have serious electronics to control the charging, and to provide various voltages out, its possible that there could be any organization of the cells. Neither 5 nor 12 volts is "natural" for Lithium Polymer, so we can't tell anything from that. I might guess its 4 cells in series ("4S") because the charger is 15 volts, but it could be anything.
This is why I always like LiFePO4 batteries (Lithium Iron Phosphate) for this purpose because the 3.2V cells in a 4S configuration are 12.8 V, which is then a drop in replacement for Lead Acid. They are also much safer, but they never quite caught on and are still rather expensive.