zero bars at last several start ups

Yeah your battery isn't worth a crap basically what it sounds like I mean it should come back on in the morning about where you left it last night as far as the HV battery is concerned so if you park it green let's say hopefully we're looking at the energy monitor first off on the display you know it goes from green to blue to a magenta color which is red pinkish. So if you park it in the green at night at shut down and it's not 50 below zero when you come out in the morning to go to work or do whatever it is you do and you turn the car on and everything was left as it was shut off the car comes on the energy monitor comes up and you see green. Then when you back out of the driveway remember that's electric only You start using juice and by the time you pull it into drive and pull up to your mailbox and get out onto the main road you might be in the full blue mode perfectly acceptable. But if you come out in the morning after parking at green 8 hours ago or so and get in the car and it's showing no bars you're saying white no magenta no green no blue it's just turned on and white yeah interesting. So somebody who tests that battery is probably going to find out that you've got some volts but nothing behind it whatever but once it's running and the generators are charging and doing whatever it can do something as in drive or what have you so what kind of gas mileage are you getting for a whole tank not just the 5 minutes that it's white you making 40 to 45 mi a gallon consistently? If I don't have any codes and no lights on the dash and decent software is telling me nothing on my handheld computer I'm probably cracking the battery case open to have a look just because seems like the inverter and the motor generators are doing their job once driving and things are running do you get to see magenta and then blue and do you green?

 

Zero bars means the battery in the energy display is completely white like it sits when you're in accessory mode listening to the radio but not running air conditioning and doing anything just sits there white

 

Start logging how many bars your at when you shut down and how many when you start up. Giving the age of the car, I'm guessing you pack is on it's last legs. If your going to keep her, start saving up for a new pack or look into trading her in before it starts throwing codes. IMHO.
A good pack should startup with the same amount of bars or more than you shut down with. You can gain a bar or two during the work day as the battery recovers from it's commute to work and warm day sunlight, but it should hold the same amount of bars when you start-up to go home.
Take the car out for a Sunday drive to fill or get close to full all bars. Park and check status the next morning. The number of bars you loose is an indication of how worn-out the pack is. You'll need to do this over a period of months to gauge it's decline, just reminder that we're heading into winter and you'll need to compensate for temperature swings too. Toss out extremely cold nights data points, because those will be outliers and you'll be losing a lot of bars on those nights and your mpg will be dropping too..

 

Your battery pack capacity is down to near 50% and you might have corrosion in the voltage sensing harness and bus bars. Parts you need can be purchased here: Hybrid Battery Wire Harness for Gen 2 (2004-2009) Toyota Prius | ACENBAY

If you don't have warning lights you can deep cycle the pack to restore its capacity up to 96%. That means you do three successively longer discharges and then full charge and balance each time. You can use the product Maxx Volts sells, or the one Hybrid Automotive sells or you can build your own: Build Hybrid Battery Maintenance Gear For Under $100 | PriusChat

This is the best overview of the problem: FAQ – Hybrid Automotive