Just curious - why Lithiums are so heavy?

pnichols wrote:
Another "problem" with Li batteries that lead acid or classic dry cell batteries don't have is: Li batteries don't smoothly taper off voltage as they begin to need recharging - they just kindof are full voltage all the time or suddenly put out inadequate voltage right when they die.

I see this all the time with the Li batteries in my flashlights. The flashlights are either nice and bright or suddenly too dim. I prefer batteries that provide slower declining voltage values as they die.

This characteristic of Li batteries could leave some RV users suddenly power starved if their Li battery systems don't include easily accessible and understandable meters indicating how many amp hours are left in the battery bank.

I think you are observing the effects of a regulated driver in your flashlights, as opposed to unregulated cheaper lights that gradually but continually taper down the output. A good regulated driver gives you the most runtime possible with consistent lumens, then it steps down to the next lower level and repeats the process. If you prefer the dimming action of "vampire circuits" then you can buy cheaper lights and save some money. But it has nothing to do with lithium batteries. One can roughly estimate the remaining charge of a Li-Ion by measuring the voltage... something like 4.2 is full, 4.1 is 90%, 4.0 is about 80% (IIRC the percentages), etc. My point is, the voltage does decline with use, but the regulation circuit keeps you from seeing the decline until it reaches a set point.