2004 Prius ECU programming?

You're flying blind. The car has error codes which will tell you much. You can go to a Toyota dealer or hybrid specialist to get the codes read or you can get a (cheap) aftermarket copy of Techstream and and a correct OBD to USB cable that can connect to an older PC laptop and read them yourself. Tons of info on the latter.

If the car is on the original battery, I'd highly suspect it.

GOOD LUCK!

 

P0A80 is for a failed battery.

Folks have successfully swapped in a complete used battery which includes the HV battery ECU inside.

 

Yes. When the battery has failed, the ECU's will direct the engine which isn't designed to carry the full load to carry the full load so it runs very, very high trying to compensate. You should also be hearing the HV battery fan in the backseat area running full speed too. Classic signs of a battery failure.

Here's what I did when mine failed and outlines ones choices: My P0A080 fault code and battery rebuild | PriusChat

GOOD LUCK!

 

Oh don't thank me, than PriusChat. I learned it all here.

Note: if you look at my opened battery pack pic that has the bright yellow volt meter sitting on top, you can see the battery ECU just to the left of that. It resembles an old computer hard drive in size and shape. There have been a few reports of its connector frying and causing trouble codes. FWIW

 

I like this thread. Consider it the bible & originator. Read & take notes to supplement your knowledge.
Gen II Prius Individual Battery Module Replacement | PriusChat

FYI:
A module replacement has short term longevity.
A rebuild has better longevity.
A new OEM HV Battery ($2071) will give you the greatest longevity. If one does not have $2K, that's a different issue.

Some people ardently disagree w/ me for wanting to spend $2K on a new HV battery. These people fail to see or comprehend the complete picture:
1) The HV Battery is quite portable. It can be transferred into another Gen2 should something happen to the current car (cost prohibitive repair or accident that does not damage the HV Battery).
2) You could upgrade to a Gen3 by swapping the modules into the Gen3 HV Battery case, should something happen to the current car (cost prohibitive repair of accident that does not damage the HV Battery).
3) The car is worth very little, say $2-$5K. Its foolish to spend an amount equal to or 1/2 the cars value. Keeping the current car running, if its paid for, in sound operating order, and decent exterior condition, is far cheaper than buying a replacement new or used car, esp with a loan.
4) Don't forget, the HV Battery is a consumable item just like tires; granted tires are far cheaper. No one balks at having to shell out say $50+/tire (and this is on the cheap end of tires), on a regular basis. One can buy a used tire, but few people do, b/c they know a used will not last as long as a new tire, in addition to a safety factor of buying used.
5) Hidden costs of a rebuild (DIY or from companies such as Doorman or Fraudtech (Greentech)):

If you can't DIY the install, you are paying someone to do it.
Do you have access to another vehicle while you are waiting for the warranty replacement or doing the rebuild? If not, walk, public transport, Uber/Lyft, or rental car it will be for you.​

I place a premium on reliability and unnecessary maintenance. Swapping a module or rebuilding every so often does not sound fun to me; not to mention getting stranded. $2k is a small price to pay given the longevity of a new OEM HV Battery. If one amortizes the cost, over the service life of the HV Battery, the costs are cheap. I am still on the original battery, 9years, 156K miles. Lets just say the battery dies in year 10. $2071 + tax ($186.39) = $2257.39/10years = $225.74/year /1year/12months = $18.81/month / 1month/30days = 63 cents/day. You can amortize the cost over miles to see operating costs; but same concept applies, the longer the part lasts, the cheaper its operating cost was.

We each have limited resources (time and money). Spend as you see fit.