Enjoy all the features of the steripen adventurer opti water purifier and drink safe water on or off the grid. solar charging clamshell case pulls double duty, recharging the included double-cell rechargeable rcr123 lithium battery and providing handy, secure storage for the water purifier. simply clip the charging case onto a backpack or set it on the ground and aim it towards the sun to recharge the double-cell battery empty charging case weighs 6.8 oz. solar panel recharges 1 double-cell battery in 2 - 5 days, depending on solar conditions battery can be recharged via the included plug-in power adapter in 4 - 6 hrs. the adventurer opti water purifying device works with containers with a minimum 1.75 inches in diameter.