top-up 
noun British
1An additional or extra amount or payment that restores something to the level that is required: they will miss out on hundreds of pounds worth of pension top-ups [as modifier]: top-up fees for university students...
- Starting to suffer from taxi lag, but champagne top-ups soon restored energy levels.
- It is well stocked with crucians and tench and has just received an additional top-up of big crucians.
- The usual charge per tyre is between £1.50 to £1.75 for the initial fill (because the tyres have to be removed and cleaned), after which top-ups are free.
1.1A quantity of a drink that refills a partly full glass or cup: he headed back to the bar for a top-up...
- There isn't even someone waiting to top up my coffee.
- Pour in beer stir and serve with remaining beer for topping up.
- Strain into two glasses and top up with champagne or sparkling wine, depending on preference.