The tenth time you get through the charges the secondary is now cheaper.
Only if your time is free, especially with that single slot charger.
Let's use a test case of a week of nights using cells, say, 80 hours of darkness. For 80 hours of use, you could pay close to $80 for primaries for the whole week, assuming you're using that much capacity per hour.
With 18350 secondaries, the first night is going to cost you $110, and you won't have enough time during the next day to recharge them all unless you get a couple
full-sized chargers. Let's say you get a deal and can get a couple chargers for $30, now you're up to $140. But if you want your secondary cells to go the distance, you're resting them for a day after charging, so you need another $110 worth of cells for the second night. That's $250. And that isn't counting the cost of the electricity, which also isn't free, but should be negligible compared to the bottom line for a few weeks use.
So it's only after three weeks (
of using cells for light all night long) that the cost of primaries catches up with the greater initial cost of secondaries.
If you're a flashlighter, secondaries are the way to go, will be cheaper and more environmentally sound in the long run. But if you aren't using your light every night, if you use a flashlight like most ordinary people,
it may take years before the low initial cost of primaries catches up with the higher initial cost of secondaries. Some use a flashlight once every 6 months for 20 minutes. In this case, primaries would be the only economically sane option.
It depends on the task, and the time it takes to compete the task, and how many subsequent flashlighting tasks are expected, and how often.
