Throughout the day do you just leave the phone in the Divevolk and recharge when going to bed?
I'd say two 60-70 minute dives leaves you around a 35-40% charge remaining, which is actually pretty good, and I've left it in the rinse tub between a first and second dive. However, you set the phone to never-sleep, and so the battery drain is constant, and I'd say best practice is to take it out during surface intervals, both to avoid any thermal stress and to do a quick charge (and to have the phone for pictures on the boat or of the scenery). If I'm on a day boat, I toss in a USB power pack just in case, bt I've not used it much. If I was doing 90-minute dives I'd put it on the power pack for the surface time.