Ideally one that doesn't drain almost as fast off (properly powered off) as when on? When fully charged it's doing its job and survives quite happily for my typical 3-4h rides but for some reason it has this constant battery drain meaning I've grabbed what I think would be a fully charged unit to find it has virtually no power left. I don't understand this as it's a lithium ion battery which should only lose 1-2% of life per month. My device goes fully flat from full in under two weeks. The device is two years old and I ride about 3000 km per year.