Never keep a full charge in your Pearl battery for periods of time, this will cause its capacity to decrease by about 20% per year. Instead, when you don't plan to use it for a while, discharge it to around 40% - At this charge level, lithium-ion battery degradation over the course of the year is around 4%. However, be careful not to over discharge your battery before storage as deep cycling also reduces maximum battery capacity - Hopefully this should not be possible unless you disconnect the battery and manually discharge it.

When not using your Pearl, keep it in the fridge, but don't put it in the freezer as freezing it will also adversely affect the battery maximum capacity.

The best results are achieved below 10 degrees celcius, although most of the data available is at 25 degrees since this is around room temperature, temperatures above 40 degrees celcius appear to be bad for the battery, the ageing process is accelerated at temperature and not in a linear fashion.

Note that this is NOT the official Rio line on batteries, but the results of my own research on Li-Ion batteries in general.