Should my battery get this low?

What you describe is normal. The SOC (State Of Charge) for the battery can swing up or down in just a few short minutes when driving. It will stay fairly level when cruising along, but if you change driving conditions the SOC will also change. Hill climbing is a good example.

The battery SOC shouldn't change a lot while parked overnight. Small changes are normal, since the displayed SOC is an estimate based on many factors, but if the SOC goes from green to purple overnight, that would be a cause for concern.

Tom

 

My charge does flucuate fairly quickly. I wish I had another Prius to compare it to. I'm keeping a closer eye on the battery level now. There were five bars when I parked this morning, I'll see where I'm at when I power up tonight. Hopefully there are still five!

Thanks

 

Hi Dave,

Well, another fun project to add to the Prius maintenance list might be to remove the trunk interior trim so that you have access to the traction battery; then pull the orange traction interlock switch and remove the covers to see what the battery modules and the busbars look like. If you find corrosion on the terminals, clean it off, and then retighten the nuts that secure the busbars to the modules, that might give you an extension on the life of the battery. (Significant shock hazard involved; if you want to do this you'll need access to the repair manual docs at techinfo.toyota.com and carefully observe all safety warnings.)

Or you could just buy a replacement battery from a salvage yard; last time I looked 2G salvage batteries were selling for ~$400 plus freight.

 

It's important to remember the battery heats up a lot in use. The voltage of a NiMH battery varies as much from temperature changes as it does from changes in SOC, so small changes in the SOC bar graph overnight should be considered normal. The graph/battery computer uses measurements of power out vs power in and voltage to estimate SOC. There may also be some temp. compensation. Going from green or almost all blue to magenta when OFF overnight is NOT normal as stated above. A drop of one or two bars is common.

The dealer can do a test to read out the battery module pair voltages to see if one is in trouble. This will cost you $50 to $100 if not in warranty. I'm not sure if they would do it covered by warranty without a code.

Basically you would expect a battery to loose one or two modules first, not all of them at the same time. A bad module (even from one cell) can interfere with the charging and discharging of the battery.

The 2004-present model is just getting 5 years old, and I wouldn't expect to see battery problems becoming common for a few years yet. It's still possible for the odd one to fail due to a rare bad cell (leak, contamination, etc.).

 

The battery module voltage test might be the best way to get peace of mind. Individual modules can be replaced, much cheaper than replacing the entire battery.

In any case, don't let the battery overheat. Do use the A/C in hot weather, and don't obstruct the battery cooling vent (to the right of the rear seat).

 

Thanks for all the information!

I read somewhere you can get one day access to the Repair Manual on the toyota site, and you can download the entire manual. Then you don't need to go back to the toyota website.

Is this correct? If so, is that easily done?

Thanks,
Dave

 

So I see from another thread that you can download the manual, but it may take a long time to do it piece by piece. Is this true with the 2004 manual?

 

techinfo.toyota.com requires you to download many .pdf files. One business day access, if you sign up on Friday, will probably give you access until the following Monday. In my case I paid $50 for one month access to have plenty of time to explore the site, and download the New Car Features manual, the electrical wiring diagram, tech training info, etc.

You should make it a point to download the NCF for 2004 because this provides "theory of operations" that the repair manual does not provide. The latter tells you what to do but not why you are doing it. NCF provides you an overview about how the hybrid components function.

Note that the repair manual by itself is >4,000 pages. The EWD is several hundred pages.