Just got a used 2012 Prius TWO, NOT II, yesterday, I noticed that the battery on the dashboard was down to two bars when I was driving at one point. What happens if it goes to zero bars?
congrats and welcome! it doesn't. it shuffles between two and full. two is still about 40% battery left, and 'full' is about 85%. toyota limits the upper and lower ends, but you don't see it without a scan gauge. all the best!
When you have two bars left, the engine will start to charge it up. This is usually around 40% state of charge according to the scangauge - the car doesn't let it run down further to extend its life. You won't see one or zero bars unless maybe you are in neutral or something is wrong.
You don't want to know... More seriously, can you describe how/when this occurred? It'll happen with a normal battery sometimes, under conditions where the car is able to stay in electric-only mode. Then, it's happy to eat up the charge. A couple of cases where this might happen: 1. Protracted stop-and-go traffic, at a crawl. 2. Low speed hill-climb, for example: spiralling up through a parking garage. (This one gets our battery down to 2 bars, every time.)
Mandel is right. Mine gets down to two or even single bar when stuck in stop-and-go traffic. As long as the charging kicks in, there shouldn't be any concern at all.
And to actually answer the question, "what happens when it gets to zero bars?", usually the engine begins to charge it back up. ASAP! Nothing bad happens. The HSD just doesn't let it stay that low very long (it's still at about 30% charge at zero bars). The system tries to keep it about 60% charged, but will allow it to go to full bars on rare occasions (and will aggressively try to drain it back down) and rarely, to zero bars.
Same answer, "the engine starts". And it's easy to do this: just sit parked somewhere with the air conditioning running. The battery will discharge and then the engine will charge it back up. Rinse, repeat; watch your MPG figure slide
I've rarely if ever seen that display down to one segment, and see all eight only on big downhills. Mostly, it tries to stay at six.
I've seen it hit eight, coming down a ski hill. And then for a bit it starts doing magical stuff, sometimes, like staying in electric-only even when you push the accelerator hard enough to pass the median point on the bar of the Hybrid Synergy Indicator.