I find that if I leave a 'null' in my BL700 it'll eventually un-null itself without further intervention.
As mentioned elsewhere, I used to find crudely charged batteries a hindrance. They'd take umbrage and I'd be changing the batteries in my Apple wireless stuff every couple of days. The BL700 changed my life, probably more so than the time I started to wear a dress and call myself Samantha, and now I change batteries every couple of months. And wear trousers again. Thank you, BL700!