Originally Posted by HarryT
Lithium Ion and Lithion Ion Polymer batteries are alike in that respect - neither of them minds being "topped up", unlike older battery technologies where it did harm the battery not to fully discharge/recharge it.
I'd be very surprised if it wasn't a lithium ion polymer battery; they've almost completely replaced the older lithium ion technology.
All the current Sonys are ion battery but the Kindle is polymer.
A quote from the repository of all human knowledge (Wikipedia) on Lithium-ion battery (without the polymer bit).
* The rate of degradation of Lithium-ion batteries is also related to battery charge level; they degrade much faster when at 100% charge, than at lower charges. Since batteries die if deep discharged (depleted) and since a battery has some self-discharge it is frequently recommended to store batteries at 40% charge level.
I'm just going to buy a 40%-ometer.