Glad to help as much as I can nurit and Grouch. When using the Steripen for trips, if you only put the batteries in the unit when you need it, it will save battery life a lot. I think it has a small current drain on the batteries if left in there all the time. The solar recharger they sale with the steripen takes forever to recharge and a fold able cell is a invaluable tool. I did find out that my 40 watt cell will power the steripen with no batteries vs my 20 watt won't. But both cells will charge the batteries quickly and if you keep some spares around and there is a sun out to recharge then you will be ok. I do like the 40 watt cells in case I have battery failures or no sun for awhile and I need power now, when the sun does return from multiple rainy days, and the battery power is low so I can just run the steripen off of the cell with no batteries for quick treatments.