TabletKiosk Sahara Slate PC i575/i535 - Manual (Page 51)

Chapter 03: Battery Usage and Care 25
For optimal longevity of the battery packs, it is important to
periodically charge them in order to keep their electrons mov-
ing. Even charging the batteries for ten to fifteen minutes every
60 - 90 days should be sufficient to keep the batteries in good
condition.
Since a battery will slowly discharge during prolonged storage,
you should fully charge it before using it again.