Rockbox General > Rockbox General Discussion

Wondering about iPod Battery

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Llorean:
A lithium-ion battery that's stored full, at room temperature, can lose up to 20% of its capacity per year. That's 1.7% per month. Even dropping that down to 1% per month (assuming cooler temperatures, and storing at an better level than full) you're talking about losing 4 minutes of battery time in Rockbox per month, just from self discharge. Which means if Rockbox were to be gaining 4 minutes per month from optimizations, you wouldn't be able to see it.

And of course, depending on how much heat you exposed your iPod too, how many charge/discharge cycles over the month, etc, the numbers could vary.

It just makes it very hard to compare your own iPod over time with itself (and it's impossible to compare with another iPod). You have to compare your own iPod to its retail software, and of course they don't provide a good benchmarking tool. :) This is why measuring small battery life changes is ridiculously difficult.

In theory, you could run a bench with a month old version, then immediately run the same bench with the current version, so that you're comparing the older one to the newer one on the same day, and use that method to sort of chain the benches along, in pairs. That would give you somewhat useful results from month to month.

soap:
Measuring battery-runtime, regardless of repeatability of conditions is really an indirect way to measure what you really want to know.
You want to know how many amps (or fractions thereof  ::) ) the player it drawing under a variety of conditions, and compare those numbers to the stock firmware.
Note that according to the tests in this thread:  http://forums.rockbox.org/index.php?topic=8867.msg68613#msg68613
Rockbox at idle is consuming 165% of Apple Firmware at idle.
All the code optimizations in the world won't solve (what appears to be) a large chunk of the problem.

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