Originally Posted by wphamilton

I have to take issue with the math. The 3-4 "lifespan" in this case is the total amount of discharged electricity over the life. Therefore the total cost should be per ampere-hour, and at 4 times more for even double the price is a huge savings over time.

Taking this a step further, there are two ways to only use (for example) 60% of the battery. One is with a full charge and discharging it only to 40%. The other is only charging it to 60%. These two are not the same with respect to battery life, and we should actually take the range from the middle - the 60% would be from charging it to only to 80% and discharging to 20%. This last is the recommended policy and, apples to apples, results in the battery having five times the total use of electric power over its lifetime.

You'd be WAY ahead doing it this way, with the only downsides of carrying more battery and as someone mentioned, the battery still being alive in a few years when you want to buy the latest greatest. I'm not sure I buy the latter as a reasonable objection - batteries aren't changing all that fast, that you'd feel like your pack is obsolete in three years.