On Tue, 03 Jun 2014 06:38:33 -0700, dave
wrote:

On 06/02/2014 04:46 PM, Jeff Liebermann wrote:
On Mon, 2 Jun 2014 12:27:57 -0700 (PDT), wrote:

But anyway, one of these dayds I might be in a situation where
it is to my advantage to take a bus or rapid (the name we sue
for something like the subway here) and it would be nice to
have the laptop at least last the ride. But that is not now
so it is not a big issue.

My new $150 Acer 720 Chromebook battery lasts about 8 hrs of
intermittent operation. I haven't timed it, but it easily lasts all
day without a charge. That seems to be the trend in ultrabooks and
tablets these days, where the battery is something like 75% of the
volume of the device.

Lithium Ion cells discharge unevenly, some cells supply more current
than others and the inverse is true for charging. Something must be done
to "equalize" them, kind of analogous to series silicon diodes in a
power supply. My friend has a high tech lithium battery for his Harley,
it has a computerized charger that balances the cells. The battery will
still start the bike on an alternator charge, but the battery is peaked
out by the computer charger. Not all battery packs are equal.

Very true. The RC (radio control) industry figured that out long ago.
Almost all the available chargers are the "balance" charger flavor,
where each cell is individually charged (at the same time).
http://www.rcheliwiki.com/Balance_charger
http://www.hobbyking.com/hobbyking/store/RC_PRODUCT_SEARCH.asp?strSearch=balance+charger
They even standardized the charging connector. Maybe some day the
laptop industry will do the same, although they're probably making too
much money on replacement batteries to worry about improving the
product.

One oddity is that the RC industry stuffs rectangular prismatic cells
into cylindrical shaped (aerodynamic) vehicles, while the laptop
industry insists on stuffing cylindrical cells into rectangular boxes.
It boggles the mind, but such tradition and stupidity are difficult to
cure.

Incidentally, I've rebuilt a few NiMH battery packs for power tools by
replacing the cells with LiIon and charging them with RC model balance
chargers. Mostly, I just buy the fairly cheap 11.1v 3S1P battery
packs and cram them into the gutted plastic battery case. Something
like this (which I had hanging around):
http://www.hobbyking.com/hobbyking/store/__14987__Turnigy_1300mAh_3S_20C_Lipo_Pack_US_Wareh ouse_.html
Notice that it comes with the standard connectors. I've only done two
battery packs so far, but my initial impression is favorable.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558