1. You are correct in that we guarantee a shelf life of 5 years but from experience they will exceed this by some margin. I recently tested some which the MoD had kept on a shelf and basically lost them. They were 9.5 years old and we tested a sample batch to over their full nominal 250 litre capacity as we were concerned because they were going to send them out to Afghanistan. They performed perfectly so we were were able to give them a clean bill of health. I get this question quite frequently and I start to get nervous at 10 years and recommend replacement as a matter of course.
2. Once you have used a unit/set of filters then all you should do is pump it out and preferably let it dry out before storage and it will then be good to go next time you want it even if it is months or even years later. The only caveat to that is that I usually suggest discarding the first half litre of water as we would advise when the unit is new and first used.
3. The other question we often get is, "my unit rattles when shaken is it OK?" - Yes it is, this is normal as there is a non-return valve which contains a small stainless steel ball. Without this the unit would simply not suck and pump.
4. The other one which often gets asked is "when do I know when to change the cartridges" - The cartridges are designed to start to block and the unit become hard to pump long before the biocide is exhausted. They have been tested to beyond double their nominal capacity and still performed effectively. Life expectancy is governed by the clearness of the source water and we always say to use the clearest source water available and try to avoid the proverbial 'muddy puddle' if possible.