Hybrid Battery Expected Life

Can't speak for the others, but my assertion was that you should expect to replace your battery at about the same time you replaced your transmission and differential in your Corolla (or Other car). For most owners this equates to NEVER.

11011011

 

You are in California so there is 10 years / 150,000 miles warranty. Even if your warranty runs out after 2016, imagine how much the replacement battery will be. It will definitely be lower as Toyota just dropped the price this year.

 

It will most likely never fail. Anything is possible but the most likely outcome is supreme happiness.

 

There have been three generations of Prius batteries:

NHW10

• "D" cells welded into 6-cell strings
• Many are reported failing
• Current activity in NHW10 groups are discussions of how to buy and build replacement battery packs
• NHW11 "D" cell prices have fallen but still expensive

NHW11

• Prismatic, 6-cells per modules with common vent for all cells
• US Gov. endurance test: 160,000 miles, 6.5 Ahr -> 2.2-2.5 Ahr
• Ending miles per gallon close to average
• First 3-4 months had higher mileage, 2-5%, but significant
• Continue to see failures but salvage market or Toyota repairs keeping up
• Evidence of weak pressure joint at terminals
• High temperatures and a lot of regeneration seem associated with early failures ... heat is the enemy

NHW20

• Similar prismatic, 6-cell modules to NHW11
• Thicker plastic and improved terminals, no evidence of weak pressure
• Not plug-and-mix with NHW11 modules, may replace all NHW11 modules
• Lower internal resistance, lower total pack voltage
• Same 6.5 Ahr capacity per module (may be higher due to lower resistance)
• Extremely low failure rate
• No one has done any life-cycle Ahr measurements

SYNOPSIS

The NHW20 modules are clearly superior to the NHW11 modules. Given a choice between replacing an NHW11 pack with NHW11 modules or NHW20 modules, I would go with NHW20 modules HOWEVER they need to be matched.

The NHW11 modules tend to suffer most from heat induced failure. So far, failed battery packs tend to show: 1-2 modules with shorted cells, unrecoverable, the rest are very low capacity but water refurbishment seems to work. Although the modules may be re-sealable, the weak terminal seals make this suspect. No refurbished modules have been through adequate pressure testing!

We suspect the other model, Toyota hybrids have been using other, experimental battery module layouts. So far, the number of vehicles and availability of failure reports has been inadequate. Furthermore, we suspect these other vehicles may have slightly different control laws with different battery management rules.

We know that GM's great 'invention' for their Volt LiON battery pack is active environmental controls. The battery pack and housing uses the charge to maintain a safe temperature range and the other control laws watch to avoid doing things that might trigger a failure.

NiMH batteries are more sensitive to care than traditional lead acid batteries. No form of voltage limited charging should ever be used. However, they carry a substantial amount of energy in what is relatively robust form. Certainly compared to LiON, these things are bricks!

SPECULATION

It may be possible to operate NHW11 modules in a non-pressure sealed but isolated from the atmospheric mode at like new capacity. Degassed water (there can be no CO_{2}!) can be replenished and overcharge O_{2} safely vented through an air trap. The plumbing is non-trivial but this should provide improve MPG for an NHW11 with unlimited battery life.

We can find no other failure mechanism other than water depletion as explaining the non-accident, module failures.

Bob Wilson

 

To visualize the battery modules as mentioned by Bob, I am attaching the pic that sums up.

 

Hi All,

Very good info on gen 2 battery life. It seems heat can be an enemy of long life. How about little use? I'm looking at a 2004 with only 10,000 miles. The car looks new and the dealer is asking $19,000. The price is clearly too high. But is it a good bet for long traction battery life? Or is it more likely to expire soon after the 8 year warranty and never make the 100,000 miles?

Thanks, Dan

 

There is no evidence of time causing a loss of electrolyte but we do know the NiMH suffer from 'self discharge.' In theory, if an NiMH were under utilized, the self-discharge _might_ lead to a loss of capacity BUT we don't have a good model for this. Please don't use this speculation as a 'hard call.'

One of the missing battery techniques is a way to measure battery capacity. There is only one field test that I think has merit but it is a little exciting:

• force charge at the bottom of a large but shallow hill
• use "R" to slowly backup the hill until the car stops
• use the altitude change and mass to calculate battery capacity

I tried that experiment last winter but the cop car seemed extremely interesting in why I was backup up a hill at 2:00 AM. How to do this in a way that does not attract attention remains the 'exciting' part.

Bob Wilson

 

do you mean charging with a constant low current but a changing voltage is bad with these battery's?

 

Although some claim and many consumer NiMH chargers use a low current charger and some include a thermal sensor, I have been disappointed with the results. The primary reason is weak NiMH batteries have already moved their 1 C (their Amp-hour rating based charge rate) down but the simple chargers don't have the ability to detect the new rating.

We know that operational Prius modules have a range of Ahr ratings:

• 6.5 Ahr (initial, new rating, measured, multiple sources)
• 2.0-2.5 Ahr (measured, operating, multiple sources)

There is roughly a 3 to 1 ratio of battery capacity and the equivalent "C" or charge rating. So if your charger is conservative but lacking feedback, it would need to current limit to less than 200 mA., which would be a terribly slow rate of charge.

I have considered an approach to battery tickler charging for my NHW11. The only way that makes sense is to me is a multiplex charger that cycles between all 38 (actually a dual-charger handling 19 modules each.) It incorporates the dV/dt charge limit detection only tuned to limit charging to 85% of capacity. But even so, this is tricky electronics and control.

The nice thing about this dual-charger approach is I can use DB-25 connectors, 20 lines, so the battery splitter, safety relay has no risk of an inadvertent shunt. Also, it is easier to deal with perfectly lethal 165 VDC although I would break it down into 19, 7.5 V. problems.

Bob Wilson

 

There is no reason to expect short battery life. I have worked places where we had battery powered forklifts and jacks that were used for entire shifts every day that were easily 15 years old that never had their batteries replaced. Just properly charged with computer managed charging equipment nightly. Ironically all of our Lifts were Toyota.

 

200ma? per cell i guess!?

buth thats 5,6 amps per pack!
5,6 amps will charge it in about 2 hours to 85%

 

The modules (and the cells in the modules) are series connected, so the voltage adds and the current doesn't; 200 mA per cell is 200 mA per module and 200 mA for the pack.

-Chap

 

yes but iff he charges one cell at a time
then in total you also put 5,6 amps in
28 x 200ma at 7,2volts

 

Perhaps these photos might explain the relationship between cells and modules:

Here I've just cut the top of an NHW11 Prius battery module. You can see there are six cells. Cleaning out the top, you can see the interconnection between each cell:


So when we go to charge a Prius module, all cells are in series and the charging current is the same for each cell:

The vertical impressions are the cell boundaries in each module. Electrically they are connected in series.

We do not have access to individual cell electrodes, just the two terminals on each end. There is a 'gap' between each cell that allows the electrolyte to equalize between each cell. Within reason, this should keep the cells at an equal capacity. However, one of my planned experiments is to sink probes to understand more about individual cell capacities when a module shows a failed cell:

This is the graph of the charging profile of a module with a failed cell. Since all cells are integral to the module and no external access to the cell terminals, there is no way to 'remove' or bypass the failed cell.

Let me suggest a more interesting challenge with your RC "C" cells. Take one that has failed or is weak and rejuvenate it. Now you have to be very careful because the electrolyte is concentrated KOH, lye. It will dissolve any organic material, like hands and eyes, that it comes in contact with. But using safety glasses and a handy bowl of wash water, you can work with them and see if you can recover their capacity.

It is important to have a quality charger:

I'm using an MRC 989, which has an excellent dV/dt threshold detection.

Bob Wilson

 

Is there a definitive test to determine if the battery is failing?

 

There is something similar described in the maintenance manual. It involves discharging the traction battery while looking for a voltage differential of 0.3 V and then charging it back up. The documentation is poor but the protocol involves blocking the wheels. It looks like "R" is used to discharge the traction battery and then ordinary "P" or "D" to recharge it.

Bob Wilson

 

This is probably a dumb question, but I am no mechanic so I will ask it anyway. I have a 2002 Prius with 80.000 miles. So it is just out of warranty on the traction battery (by years, not by miles). My traction battery has a dead cell (that is what the mechanic at the dealership told me). So the scary lights are on and I am told I need a new traction battery. My question: how long can I go on driving the car before I replace the traction battery? I drive maybe 15-20 miles on a busy day.

 

Patrick Wong has experience. All I can suggest is calling Re-InVolt and seeing if they have something you're interested in. It is a fairly straight forward swap if you don't want to try for Sanford, NC.

Bob Wilson

 

This is actually a very good question.

I would first ask you what driveability symptoms does the car demonstrate. For example:

1) do you notice the gasoline engine is running at all times
2) do you notice driveability issues, like poor acceleration from a standing start, or an unusually low limit to the car's maximum speed
3) have you noticed a decrease in mpg

I would also ask what DTC has been logged by your car. This usually is documented on the repair invoice.

If you don't notice any of the symptoms mentioned above, then I would question whether in fact the traction battery has a "dead cell" and needs to be replaced, at least in the near-term. Your car might have some other problem, like a high voltage ground fault, which will not impair driveability but poses a safety issue.

If you have noticed these symptoms, then I'd suggest that you develop a plan to replace the battery soon, or get rid of the car, given your daily commute. Good luck.