I use my regular phone.
My iPhone running Loop all the time lasts easily though a day. Whenever I am running navigation I just plug the phone in - that's what I'd do anyway. Even if the phone runs out of juice, this is not catastrophic - the system simply defaults back to the pump running on its own normally.
Yes, that's a problem. My loopable 523 is now close to 2 years out of warranty. Fortunately, I've never had any issues with it. Since I started using DIY closed-loop systems more than a year ago, I've been able to get another two loopable 522's as backups. My prescription is for a Med pump, and I have no issues with supplies. Longer term, one of these 3 scenarios will happen: (1) best case, a new pump will come out hackable and available to me; (2) next best case: a commercial system at least as good as DIY systems will become available (in my opinion, 670G does not pass the "as good as" test, so I'll pass on it); or (3) worst case, I'll eventually run out of my hackable pumps, and will default back to whatever new pump I can get at that time.
New models are not hackable. Looks like Veo is just a different name for MM 554/754. If so, then early firmware versions are hackable: US firmware version 2.4A or below, AU/EUR firmware version 2.6A or below.
My understanding is that Dana R pump has been hacked, and that it is available in the UK. There is a group of developers working on a closed-loop system called AndroidAPS around this pump.