I'm not following. You need more than the spool to change the spool, like two wrenches. Are they in your Wetnotes too? I'd much rather change the battery on a PPS transmitter than change a spool. But, just like checking an isolator before diving, don't you check battery conditions on your computer and your lights? Why not on your transmitter, too?But, carrying a spare HP spool and changing it is easy. There is always one in my wet notes. Carrying a spare transmitter battery is far less practical. So for expedition level planning AI fails on cost benefit.