Li chemistry batteries lose capacity with age and charging. Eventually they will no longer hold a charge, or enough charge, so they must be replaced. With an iStick, the battery is non-replaceable, so this means new mod time. Charging it before it is completely depleted probably shortens its useful working life, but by what factor I do not know. Given you have chosen a non-replacable mod, and assuming convenience and availability is important to you, I'd say charge it every day and don't worry about it until it's time to replace it. I use mechanicals all the time. A mekkie changes batteries when the vape gets weak, not when the cell is dead flat charge by the voltmeter. When the batts come out of the mod, they need to go on the charger because I can't use them again until they've been recharged. This doesn't bother me, and I haven't seen any problems doing it that way. Given the reputation of the iStick 50s, I'd not charge it unattended, no matter how often you choose to do so.