I have a used Kobo N905 Touch which is, I've read, powered by a Lithium-ion Polymer battery. I'd like to keep the battery life as long as possible, as replacing it is far from easy. Should I wait until the Touch displays a 'Low Battery' message before recharging, or does this kind of battery not have a memory effect (which significantly reduces long-term battery life if you repeatedly recharge it before it is drained)?