My Portable Dremel not working properly

Submitted to Product Talk

Has anyone had the same problem with their portable battery operated Dremel & is there some kind of maintenance I may do myself .. ?
  Hi Guys,
 Have had this new exchanged by Dremel for couple years now and hardly used as became a bit disheartened because the battery would not charge properly ( have 2 ) even after cleaning points... Sometimes would work on Low, Sometimes on High, sometimes both speeds worked for very limited time... The exact same problem with both portables ??? Thanks