S-Types very prone to battery discharge (I know from experience) and the information about coil packs as well. Invest in a CTEX charger/restorer and use it very regularly. It will help in keeping a good battery in great condition.
Best Wishes and Regards, John
May just be your battery voltage being slightly low or a bit of moisture around the coil pack area.
Either way, charge the battery first and then see if it happens again.