Maybe it was the only one charged?
I dont know that this is the case, just something that would cover this.
If it is true that DB was manually programing numbers from two phones into the borrowed phone then they all had to have a charge while entering information/data.
It just seems to me that DB herself has gone into the most detail about those phones...she said they were all on the counter together, in the kitchen, because she had been programming them. She was the person who said one wasn't even working, she interrupted JI, in one of the first interviews, when he said "they stole them, so, we couldn't call 911..." and she is the one who said that LE showed her a ping chart that she believed was a lie...because the phones couldn't even be used. DB is the person who had last access to the phones per her own admission. She is the one who needed to borrow a phone from one of her relatives. She said she had been on the computer and that is probably why the computer room window was left open. Maybe she was pulling more numbers, from old emails, to put into the borrowed phone.
It seems, that JP via FBI records of the phone activity, is suggesting it was DB's phone that someone was trying to use. So, then it suggests that JI's phone was the broken one? No matter whose phone was broken, no one has ever said how it got broken.
As to the phones going into the water/river/creek/whatever: They would not have continued to ping after they became saturated. And, if an Intruder stole the phones to sell them..then why destroy them?
My cell company knows when I switch out a phone. Phones are identifiable, somehow. Anyone trying to use those phones would leave a mark.
Internet searches, via smartphones, also identify the identity of the specific phone or device (IPOD Touch for example) being used...if, via wifi, a record of the open connection that was used to attempt to get online would also show up in the data history.
Verizon only recently got the rights to sell IPhones. Previous to just a few months ago, IPhone users were limited to ATT as their carrier.