The life expectancy of lithium batteries in recreational use is, more or less, independent of charging cycles. There is no memory effect either, i.e. you can fully charge them after each trip irrespective of the charge status shown in the display.
Generally speaking, a capacity loss of approx. 4 % per year is to be expected. Capacity loss will, however, accelerate if the battery is permanently exposed to heat. Also storing the battery always fully charged will accelerate ageing. There are no concerns about using the battery in high temperatures, we recommend that you take the battery out of the sun and store it in a cool place after use.
Your battery must be returned to a Torqeedo Service Centre for service 8 years after the date of manufacture.