I've got a 2016 with over 300,000 km ( / getting close to 200,000 freedom units). Much of my local driving is on low-speed rural roads where I'm just cruising along at 60 or 70 km/h. For much of the car's life the battery SOC indicator had fairly consistent, predictable behaviour. During ICE cruising, it would stay stable at 6/8 bars, and then once it started cycling into electric-only mode, the bars would deplete gradually and steadily (as one would expect) to 2/8, at which point the ICE would kick back on. I would only see 7/8 or 8/8 bars when braking down a long hill. In recent months it seems to be fluctuating more: it reaches 7/8 frequently for no apparent reason, and will stay there for a surprisingly long time when under electric-only power, and then drop quickly to two bars. It seems minor, but it's just odd that it has suddenly become less predictable under the exact same routes and speeds I've been driving for the past six years. Any similar experiences or thoughts?
hard to know. with the nimh batteries, the gauge would start oscillating between full and empty when a cell(s) was weakening. i suppose that may be happening at 300k, but i don't know.
First you have to know if your pack is NiMH or the newer Lithium battery Toyota offered in some of the 2016 s. If a NiMH pack and the gauge stays full for a long enough time before dropping quickly to 2/8. I'd say you have a module or two or three that are starting to get weaker than the others. If you get DrPrius you should be able to see which module (s) could use some help (charge cycling ) and ( balancing to the other modules. cell 1.2 volt module = 6 cells block pair = 2 modules = 14.4 nominal volts Dr. Prius App It's hard to say how much charge cycling might help when done right OR hurt if done wrong. Babying through the warmup cycle at low speeds, leaning to slow battery regen and simple grille block when below freezing temps might help reduce the gauge drop offs some too, eventually by next spring. If it's a lithium pack it's got balancing builtin and the issue is something else. DrPrius might be able to help you pinpoint why your gauge is dropping off like you described above.
That gauge behavior is a clear sign of something not so good happening. Addressing it is recommended as soon as possible. Before the car trips a code and the hybrid system message shows up, which will likely happen, eventually. Also, keep a close eye on and time if possible the amount of time the gauge stays near the top and how long it takes to recover after it drops out. When one or both of those times get shorter, be prepared for the car to code.
