I'm considering the Freedom, only because I plan to use it on a daily basis for long periods of time and do not want to have to replace batteries. But I am concerned about Naglene bottle thread contamination, so I will also be purchasing the pre-filter that attaches to the bottle. I have seen that only the Classic, Traveler, Emergency, Journey and Defender fit into the pre-filter - so this means if I plan to use the Freedom, I will need to remove the pre-filter to sterilize? Are there any SteriPENs that work with the pre-filter and are also rechargeable? I already have a solar charger with USB port.