http://www.batteryuniversity.com/parttwo-34.htm

Quotes from that link.
"A lithium-ion battery provides 300-500 discharge/charge cycles. The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges.
Aging of lithium-ion is an issue that is often ignored. lithium-based batteries have a lifetime of 2-3 years. The clock starts ticking as soon as the battery comes off the manufacturing line.
Keep the lithium-ion battery cool. Avoid a hot car.

Here's one that suprised me. See the table after
"The speed by which lithium-ion ages is governed by temperature and state-of-charge. Figure 1 illustrates the capacity loss as a function of these two parameters."
For prolonged storage, keep the battery at a 40% charge level.

This might have bought me more time from a $190 laptop batt:
"Consider removing the battery from a laptop when running on fixed power. "

Avoid purchasing spare lithium-ion batteries for later use. Observe manufacturing date. Do not buy old stock, even if sold at clearance prices.

Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver BC. Mr. Buchmann has a background in radio communications and has studied the behavior of rechargeable batteries in practical, everyday applications for two decades. Award winning author of many articles and books on batteries, Mr. Buchmann has delivered technical papers around the world.
Cadex Electronics is a manufacturer of advanced battery chargers, battery analyzers and PC software. For product information please visit www.cadex.com.

Good link, Laurence. Indeed, the information mates well with similar info provided by NRG and other manufacturers. Thanks very much for passing it along to us.

THERE's some useful knowledge!
Thanks Laurence.

That's odd that it prefers a partial discharge.. most other batteries, such as cell phone batteries, I've heard it's better to fully drain them before recharging.

Almost no batteries like to be stored for an extended time in a completely discharged state. Partial charge or full charge is recommended. All batteries discharge during storage, but the rate is hard to predict because temperature, humidity and condition of the battery are all variables.

The article had new info for me. I'm familiar with lead batts, such as for one's car and with the well know Nicad memory effect. Lithium is like neither of those.
I've had lead batts go bad in storage (they were extras from old cars) when I took a hiatus from periodically charging them. They self discharged, then could not accept charge (sulfated?). Possibly they could have been brought back (there's a procedure for sulfated lead batts) but since I was moving and would not have space for them I skipped that. That one I've consistently kept at 100% charge is fine.
Apparantly both the chemistry and the design of a battery affect it's behaviour and lifetime. I expect to get much more out of my $200 laptop cells with the info.