P3000 among other things…

Mine is a 2007 with 360,000 miles. I’ve put 200,000 on it myself with very little repairs. I’ve probably dropped about $800 in it in 6 years. Done all my own repairs but used Toyota for diagnostics until I found Techstream. Codes can hide from time to time, but this one…
The car starts out in the morning with about 3/4 of the bars. By the time I go about a mile, no bars. Usually it recovers in about 5 miles. Sometimes it takes 20 or so. All modules in the battery are at least 7.4 volts with none being out by more than .4 volts.
Now I have all the lights and no ready…
I had a high voltage leak once and cleaned all the terminals on the battery pack, which gave me another 60,000 miles. Did this again last week and found the harness was bad. Fortunately I have 2 hv batteries and replaced the harness. Now I have the P3000 and can’t find subcodes.
when I hook up Techstream, the battery cooling fan comes on after about 2 minutes and runs more intensely than I ever heard before.
I’m thinking the battery computer. I also have a spare, but are they interchangeable without having to reprogram?

thanks…