Understanding NiMH hypercycles (to prolong Prius HV battery life)

[usbseawolf2000]

What is hypercycle?

Hypercycle is a technique to use a rechargeable NiMH battery to extend it's life cycle and maximize overall usage.

Example:

10% Depth of Discharge x 300,000 cycles = 3,000,000 overall percentages
60% Depth of Discharge x 10,000 cycles = 600,000 overall percentages

The difference is 5 times more in overall usage.


How do I hypercycle NiMH battery?

The short answer is to use it a little at a time.

As the graph above shows, you would get about 700 cycles if you use 100% at a time. This means you charge it fully and draining it until empty. Isn't it how you use those rechargeable AA NiMH batteries? Yes, the worst possible way and now you know. If you discharge it at 60%, NiMH would be good for 10,000 cycles! That's more than 27 years if you use one cycle every single day! This gets better with 50% depth of discharge as it would double the cycles to 20,000. A little dirty secret NiMH battery charger and rechargeable battery manufactures don't want you to know.


How does Prius use the NiMH traction battery?

Prius normally uses less than 10% at a time. It is also known as one hypercycle. Prius HV battery is used when the gas engine is inefficient and therefore unlike an electric vehicle, no more than 10% is usually used at a time. This understanding enables NiMH to last 300,000 cycles! Toyota has warranty for 10 years or 150,000 miles on the pack. This means, Toyota believes an owner will average 2 HV cycles per miles. If an owner averages 1 HV cycle per mile, the HV battery pack would last 300,000 miles! If an owner drives mostly highway and use only 0.5 HV cycle per mile, it should last 600,000 miles!

See below link for more:

http://sites.google.com/site/usbseaw...h-of-discharge

I finally got some time to write up what I learned and studied about NiMH over 5 years. I came up with term "hypercycling" to easily explain why Prius battery would last a very long time to those acquiring minds new to hybrids.

I am sharing information here to learn from many knowledgeable people. I am no expert but the information is what I believe to be accurate from my experience. Feel free to contribute your thoughts.

[DaveinOlyWA]

great info and pretty much the way lead acid batteries works which leads to the
" great lie" EV car manufacturers are perpetuating. my EV was supposed to have a range up to 40 miles well that was at 25 mph. that was too slow, so i had the thing reset to do 35 mph. well, that dropped the range to just under 30. that was ok, but soon realized that my batteries were starting to fail and that happened in less than a year. batteries replaced, started charging at work so now, i rarely use more than 50% of my charge before recharging.

so far so good.

Li does not have the charge life issues, only the cost issues. not putting any more money into the Zenn, holding out for a highway capable EV that will do at least 100 miles

[2009Prius]

So I suppose it is bad for the battery life to run it down to 3 to 4 bars as opposed to keeping it at 6 bars?

[DaveinOlyWA]

Originally Posted by 2009Prius

So I suppose it is bad for the battery life to run it down to 3 to 4 bars as opposed to keeping it at 6 bars?

no, not necessarily. its says best option is a 10% discharge. it does not mean 100% to 90%...in fact, pretty sure fully charged is not good either.


10% can also mean running from 70% to 60% which i think you will find is just about where your Pri spends most of its time. on a Pri... well, at least on the classics, 8 bars is 80%, zero bars is 40 %...

running between 6 bars to 3 bars is probably around a 15% change give or take.

[Patrick Wong]

This seems to support the notion that owners who live in mountainous terrain can expect shorter traction battery life. I live at 1,100 ft elevation and have had two battery failures (thankfully covered under the hybrid system warranty) out of three Toyota hybrids.

The 2004's battery hasn't failed yet but it cycles daily from eight green bars down to two red bars. The SOC is moving up and down more quickly than in the past, which implies reduced battery capacity.

[TKY]

So for those of us who are not the science types and not the math types, and who are new or recently new to Hybrids & Prius specifically, what does this mean in terms of our everyday driving? At lower speeds, say 40 mph and below, can we effectively control the battery discharge? I think this is different from controlling the point in acceleration when the gas engine engages by aggressive take-offs, jack-rabbit starts, or other fuel inefficient practices.

Thanks, TK

[usbseawolf2000]

Originally Posted by TKY

At lower speeds, say 40 mph and below, can we effectively control the battery discharge?

Below 40 mph, Prius can use HV battery pretty aggressively in S4 (for the Iconic model) to keep the ICE shutdown. To extend the battery life, do not accelerate with battery power for more than 5 seconds, just press the pedal harder and use the ICE instead. I normally limit it to 2-3 seconds and I don't press the pedal close to the threshold.

My calculation indicates that 10 seconds of battery acceleration (near threshold) uses 5% of the pack. It is almost as hard on the pack as doing 0-60 floored acceleration.

To understand how many percent each block of the battery represent on the MFD, see the graphs below from Wayne Brown's site. More information with scenarios are available in the link I provided in my original post.