TfL makes it easier to top up Oyster cards while on the go — Transport for London — “Next month, the new TfL app will launch, allowing customers to top up their Oyster card with pay-as-you-go credit and buy Travelcards wherever they are… It will also allow customers to check how much credit they have on their Oyster card and also provide, for the first time, a ‘low balance’ alert direct on their mobile to help customers ensure they have enough pay-as-you-go credit before they travel.”