For the D1 battery pack (EN4) what's the proper way to store the battery for several weeks to maximize performance and longevity? One of my two three-year-old EN4s has bitten the dust of late. It has only had approx 25 charges put through it, with long periods of inactivity at times. I've recently gotten some new ones and I don't want the same thing to happen. But realistically I don't use the D1H every week.