I have been searching for the best to charge an iPad battery and found this bit of information on www.apple.com/batteries
"A charge cycle means using all of the battery’s power, but that doesn’t necessarily mean a single charge. For instance, you could listen to your iPod for a few hours one day, using half its power, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two, so you may take several days to complete a cycle. Each time you complete a charge cycle, it diminishes battery capacity slightly, but you can put notebook, iPod, and iPhone batteries through many charge cycles before they will only hold 80% of original battery capacity. As with other rechargeable batteries, you may eventually need to replace your battery."
According to this information whatever the charging behaviour is, it will likely not affect the battery lifespan. Because one complete cycle is needed to affect it and one charge does not mean one charging cycle (according to the article).
I'm not a battery expert, so can someone confirm that this is correct?