[Arm-netbook] flying squirrel conundrum

[Benson Mitchell]

On Wed, Nov 28, 2012 at 11:15 PM, Zooko Wilcox-O'Hearn <zooko at zooko.com> wrote:
>
> If you already own a charger, then rechargeable AA's are probably
> better for you than traditional lithium batteries. Consider: a single
> modern high-capacity AA would have 2100 to 2700 mAh — comparable to
> that 3200 mAh EEMB (especially after the latter degrades with time and
> use) — would weigh the same (30 g), would be smaller than the EEMB,
> and best of all it would be cheap and easy for the consumer to
> replace.

But that 2700mAh AA has only 1.2V, whereas Li-ions (in the most
common varieties) have 3.6V -- so you need *three* AAs to match it,
and your interchangeable-cell pack actually weighs 3x as much & is
much larger than the Li-ion.

And then there's the additional complexity of a multislot battery
compartment with a door/cover that endures daily battery replacement
to charge those AAs (much worse than a user-replaceable Li-ion that
is a single piece and might be changed once a year), or finding a
*reliable* way to detect chemistry so we can charge NiMH battery
within the device, but avoid recharging alkaline or lithium primary
cells.

> I would say that the right comparison is not between a brand-new
> lithium battery and brand-new rechargeable AA's, but between the
> laptop battery that people actually use and the rechargeable AA's that
> people actually use.
I agree on this.
> I'm pretty sure the latter have superior
> capacity, because they are cheap and easy to replace. The former — the
> laptop batteries that people actually use — are often worn out, and
> are expensive or impossible to replace.
But I disagree on this. Because you forgot/didn't know to include
voltage in your comparison, you're penalizing Li-ion by a factor of
3.  In reality, even a battery with ~50% degradation is not very far
behind NiMH AAs -- but more importantly, Li-ion cells degrade much
faster with elevated temperatures, so your laptop has likely been
rather harder on them than an EOMA68 tablet or netbook would be.
15-inch-macbook-pro

> As far as marketing goes, maybe offering to run on AA's (at least as
> an option?) would be good! It would provide something tangibly
> *different* about this product.
As an option for machines with a click-in battery pack, it's great:
it'll be bigger and/or offer less runtime than the standard Li-ion
pack, but that can be worth it for the flexibility out in the field.
While I do *like* interchangeable batteries (I'm even working on a
replacement back cover for my N900 which will take two ICR18650
cells), I just can't see AAs as a solution for the low-end BOM under
discussion here.


Benson