Received my 510 Wednesday as a replacement for my DSE901. I love it but I have some questions. The kit came with 2 attys. I tested both and they both work. Do I use one full time and let the other one sit or should I rotate them? Do I let the atty dry overnight on a paper towel? After the batteries are fully charged how long can they sit unused without losing charge? I ask this because I've been using the USB pass through and I don't want to charge the batteries if they don't need it since they can only be charged so many times before they die. Thanks in advance!