Complex sentence: Some Solar Dial switches have a clockwork or battery'reserve' to maintain the time accuracy in case of a power outage, if this is not fitted the switch would require the labour-intensive task of being reset every time the power fails.
Split into simpler sentences: Some Solar Dial switches have a clockwork or battery'reserve' to maintain the time accuracy in case of a power outage. If this is not fitted the switch would require the labour-intensive task of being reset every time the power fails.