You can easily top up your OBU balance:

• On the Road User Portal (by credit card, debit card or by bank transfer)
  If you pay the top-up amount by bank transfer, you need to enter your customer number, followed by the complete serial number of your OBU (with a space between these two references) in your payment instruction. The procedure to top up an OBU on the Road User Portal is described in the Road User Portal User Manual “Top up your OBU”.
• Or at the Service Point (cash, by credit card or debit card)
  The procedure to top up an OBU at a Service Point is described step by step in the “Short Manual" in 15 languages: EN, FR, NL, DE / EN, HU, CZ, SK / EN, PL, RU, BG, RO / EN, SP, IT, GR, TR. This information can also be found in the “Service Point User Manual”.