ERS - One Shot Qualifying

@martyforster There are a few misconceptions going on here. Breaking it down:

• The ERS deployment is limited to 4MJ per lap from the MGU-K. The MGU-H has no limit, but you also have no say on its working and its primary function is to do away with turbo lag;
• The Energy Store – ES has a few regulations caps (Appendix 3 or something from the Technical Regulations has a handy flowchart for that), but the main limit is the weight – about 20 or 25kg. There's no hard capacity limit for the battery, and though official data is hard to come across it most definitely hold more than just 4MJ. Scarbs once said he knew for a fact that the 2016 Mercedes' battery had around 7.8MJ (2.2kWh) capacity. 
  • Bottomline is, you will never deploy 100% of your battery capacity in a single lap, no matter the session. You're limited to the 4MJ per lap via MGU-K.
• The Overtake button just overrides your current ERS deployment setting to the full 120kW power. So you've got the following ERS modes:
  • None – zero MGU-K deployment.
  • Medium – the standard setting, programmed to give you a net surplus per lap. So there's less than 4MJ MGU-K deployment obviously, and as long as you don't mess with the Overtake button you'll still be charging the battery. 
  • Hotlap – straightforward. Programmed to deploy the full 4MJ MGU-K limit throughout a lap.
  • Overtake – full beans.
• Overtake mode is disabled on quali sessions. You've got only None or Hot Lap to choose from on full quali sessions. I don't play these short one-shot quali, but it's reasonable for them to disable None mode altogether just to avoid any "god damn I forgot I had fiddled with it" moments in such quick races.

From your description, the game is working just as intended, mate.

You can't deplete a full battery charge on a single lap. The percentage and battery icons on the HUD refer to the ES state. You should be concerned about the horizontal bars to the right, as those are showing the deployment (4MJ) and harvest (2MJ) limits per lap: you should be pretty much fully depleting the deployment bar throughout a hot lap, indeed.