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I bought my daughter a 2005 Honda Civic Hybrid. One year ago the IMA battery was working and no check engine lights or IMA lights were on. Slowly the IMA battery degraded and now it doesn't charge at all. I understand some people on this forum that you can drive the car anyway. But it's doing some weird things like the air conditioner won't stay on, the power steering stopped working for a moment, EPS light came on/ went off, sometimes the radio went blank and then came back on. It had other strange lights that came on and went off. When below 1500 RPM the red battery light comes on. I took it to a mechanic and he said just drive it the way it is. I've seen some batteries online or at junk yards. Is it just the battery that needs to be replaced? Or are there other parts that need to be replaced along with it? I see all kinds of complicated parts associated with the IMA system.

This is her first car, and she hasn't even learned how to drive yet. The car is mechanically sound otherwise. And it does have close to four hundred thousand miles on it. I paid $1,500 for it before tax and I probably put about another thousand into it to make sure that it was safe.

 
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Sounds like the alternator may be failing, or the 12v battery might be bad as well. You can get replacement battery packs from different retailers

 
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Take battery voltage reading with car off with multimeter on the battery, I suspect it’s under 12volts.

Start the car and if your not seeing 13+ volts I would pull the alternator out and get it professionally checked.
If the voltage spikes over 13 volts when running then its likely just battery issue.

Every system you listed as acting up runs on the 12v system so keep focus on that for now.

 
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I thought that these cards did not have alternators, but rather a DC/DC inverter or something on the hybrid battery pack that charged the 12V system...

 
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No idea I've never worked on a hybrid

 
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Your right, it’s much bigger deal to replace the charging circuit on a hybrid setup.

So you did test the battery voltage at terminals and even with car running it was not going over 13v?