MFD showing battery SOC fluctuates

If you do not have it already then I suggest you get the Dr Prius app and a compatible OBD2 adapter to check the health of your high voltage battery pack. Rapid increase or decrease of battery charge might be an indication of problems such as a failing battery module. [Hybrid battery diagnostic and repair tool for Toyota and Lexus]

Posted via the PriusChat mobile app.

 

If the vehicle only has 138k on it (verified?), and if the HV battery is original, it might benefit from balancing and or some cycling.

 

Your battery is 16 years old, you’ve probably got some dying cells. It’s never good when the battery starts jumping around like that

 

Toyota has two options . Let them replace your HV battery pack with a new one. Or buy a complete set of new battery modules from them and you install them. That's it.

Any procedures for replacing individual modules (with used ones) and cycling - balancing is stricting aftermarket or DIY. Results will vary.

Posted via the PriusChat mobile app.

 

An easiest option would be the Prolong gear from http://hybridautomotive.com/

There are other options depending on your budget or DIY skill set.

 

I concur with the earlier responses. Your traction battery has lost most of its capacity. Two things conspire to cause this as they get old. One is that the cells get out of balance. So, when the module with the highest charge hits its top limit, the inverter stops charging the whole battery. When the module with the lowest charge hits its bottom limit, the inverter starts charging again.

Another thing is that the cells themselves lose capacity amplifying the first problem.

A Prolong grid charger can help with both of those situations. It won't make your battery new again, but it can extend the life by several years.

Where are you in FL? If you're close enough, interested enough, and want to buy and install the cable from Prolong, you could borrow my Prolong.

But the best fix, if you plan to keep the car for a long time, is a new battery from Toyota or, if you like DIY projects, a new kit of battery cells from @2k1Toaster. (http://newpriusbatteries.com)