My wife has a Honda CRV Hybrid. It is not a plug in hybrid. It charges through braking and going downhill. According to the power flow display, which is pretty geeky and cool. It is in a constant state of charging and discharging. As in, every trip will take the battery from charged to discharged as many as a hundred times.
How can any battery last any length of type with this frequent of a charging cycle?
They use much smaller batteries than a battery electric car and a chemistry that is not intended to be deeply cycled. Because the battery is regularly recharged by the engine and regenerative braking it never depletes enough to risk electrolyte breakdown, and cycle life degradation does not have a great impact. On most systems, the engine can also be directly engage the transmission when additional torque is required (usually at mid-speeds accelerating uphill), typically through a sprag clutch and simple transmission, or through a transfer case.
Stranger
I remember reading that the early Toyota systems, for example, would never deplete the battery very much -this ensuring the battery never had the deep discharges that would tend to degrade it. Someone said it never went below 80%.
I had a 2008 Camry hybrid, and after 10 years there was no noticeable difference - but basically it was a gas car, where the battery appeared to provide acceleration assist and recapture energy with braking. As a result the engine was almost always on (it was disconcerting at first, it would start when you got half out of the garage). It essentially micromanaged energy, so you got highway mileage in the city with stop-and-go driving. Also allowed the bigger Camry to have a 100cc engine, since the electric motor assisted in acceleration. (IIRC - My much smaller '95 Civic had a 1600cc motor…)
Allegedly it’s the very deep discharges that do the most damage to a battery. My Tesla for example recommends keeping the charge between 80-90% down to 10-20% as much as possible. (Although it’s not going to do serious damage if it is charged to 100% or almost fully discharges from time to time.) Some new Teslas I’ve read have LPF batteries and charging to 100% is recommended.
Charge cycles is an industry standard from the NiCd days as that was a good estimation for that chemistry. Because it’s a standard it persists in Li type batteries though that’s not a good indicator for them. Phone manufactures rate the expected cycle life by calculating the actual expected life in time the battery should have during normal usage, then figuring out how many charge cycles would equate to that.
What really matters with Li type batteries is time and temperature at the state of discharge. Basically the battery has a limited life even under ideal conditions and non-use. That life gets shorter as the battery moved away from about 40% charged (up or down), and gets much shorter at 100% and 0%. It also gets shorter if the battery is hot. This seems to be a parabolic curve, so there is a good section around 20-80% that will give a pretty decent life.
One way it can be described is the battery is slowly eating itself away from the time is was manufactured. It is like exposed metal corroding. If the state of charge is at 40% it’s like the rain on that metal has a PH of 7 (neutral) and though it will still corrode the rain won’t hurt it further. If it goes lower in the state of charge the rain starts becoming acid, the stronger the acid the faster it will corrode. If it is charged the PH becomes basic which also will corrode the metal. Not as fast as acid, but it will also corrode it more, and the stronger it is (closer to 100%) the faster it will degrade. Temperature also will speed the corrosion, higher temperature will greatly increase the rate of corrosion.
From what I’m seeing, the '08 Camry hybrid had a different gasoline engine specific to the hybrid drivetrain, but it wasn’t 100cc, it was still 2.4L (2400 cc):
Toyota also offered a hybrid electric version of the 2.4-liter engine, designated 2AZ-FXE that employs the Atkinson cycle to maximize fuel economy.
The 2AZ-FXE is an Atkinson cycle variant of the 2AZ-FE. It has the same bore and stroke, but the intake cam and pistons are unique. It has a physical compression ratio of 12.5:1.
The large valve overlap leads to a reduction in cylinder charge and reduced torque and power output, but efficiency is increased. This combination makes the 2AZ-FXE suitable for use only in hybrid vehicles, where peak torque and power demands can be met by the electric motor and battery.
Maximum output when used in the Camry hybrid is 211 hp (157 kW; 214 PS) at 6000 rpm with 257 N⋅m (190 lb⋅ft) of torque at 4400 rpm.
Everything said upthread is all true, but probably at a deeper level of detail or abstraction than the OP needs.
The OP’s fundamental mistake is thinking of e.g. taking 0.01% of the total charge out of the battery to accelerate away from a traffic light, then putting 0.005% of the charge back into the battery during braking as a “charge / discharge cycle”.
That’s not what the term “charge / discharge cycle” is meant to represent. The term refers to the scenario of taking most / almost all the charge out, then refilling the battery to almost / fully full. Those are the cycles that put material wear and tear per cycle onto the battery.
What you describe, going from fully charged to fully discharged, is exactly what the power flow display shows. It is very common for it to show that the battery is fully charged one minute, and then fully discharged the next, depending on usage. Of course, “fully” won’t actually mean “fully” but it’s far more than a fraction of a percentage point.
Basically, the charge indicators on hybrids lie. 100% probably equals 80% and it just never allows it to charge over that, and 0% on the display is probably really 20%, and it never allows it to discharge below that. Edit to add, or whatever percentages make sense, but it basically charges and discharges always in the best zone for the battery so it can support many many cycles.
Doh! Typo. 1600cc was what I understood it to be. It certainly wasn’t too powerful.
The CR-V has a 1.06 kWh battery:
https://hondanews.com/en-US/honda-automobiles/releases/release-1503019bd8a757ea08267d7944378955-honda-two-motor-hybrid-electric-system
That is 3816 kJ.
Since it’s a hybrid, it never really discharges much more than one acceleration cycle. 65 mph is ~30 m/s, and the CR-V is 1750 kg. Assuming 90% efficiency, we get 875 kJ.
That’s 23% of the total. Which isn’t insignificant. However, it means they can keep the battery in a nice comfortable range, well away from the endpoints, which are what cause most battery degradation. Just keep it in a nice 25-50% charge range and it will last many, many cycles.
Furthermore, since it uses <25% of the total, the battery itself can degrade significantly before it impacts the performance. Li-ion cells do degrade, but the rate slows down greatly once they reach ~85% capacity. That’s still high enough that you wouldn’t notice the difference in a hybrid. Batteries don’t just stop working when they get old.
Overall, I’d expect hundreds of thousands of acceleration cycles before there was a problem. The basic chemistry is probably capable of 5,000 full cycles. The partial discharge brings this to 20,000 cycles. Keeping it in the “comfort” range brings it to 80,000 cycles. And the extra capacity brings that to >200,000 cycles (very rough ballpark estimates).
Will it actually go from 0-65 MPH purely on battery power? Discharging 23% of a Li-ion battery’s capacity in the space of ten seconds or so seems like it would be hard on it. I know the battery packs are actively cooled, but given the general geometry of the individual cells (cylinder, ~3" long and ~1" in diameter), it doesn’t seem like you could remove an appreciable amount of the heat produced in the battery by such a rapid discharge event.
I’ve got a 2024 Volvo XC90 SUV which is a mild hybrid. It doesn’t appear to ever operate solely on battery. If I come to a stop, the engine also stops. As soon as I take my foot off the break the engine starts. As I step on the accelerator, I see the battery meter start to drop as I get back up to speed but the engine also revs.
The CR-V will operate completely on battery power but won’t get close to 65MPH on it. IME, the engine will kick on around 25 MPH.
I’ve driven company vehicles where the engine starts and stops at every stop light. I think it would drive me crazy to own one.
Had a Toyota hybrid for over a decade (until I switched to a full BEV recently) and as long as I didn’t floor the pedal, I could maybe make it a half or full mile without using the engine if the battery showed full. That depended on already being at a relatively low speed (20-30 mph) and not accelerating. Basically an ideal situation where there’s not much call for additional power.
No way that ever happened at higher speeds or under even modest acceleration. The engine kicks on pretty fast then.
Many of the PHEVs can definitely go longer but those batteries are also larger.
My cars have had this feature for more than a decade. To be honest, I don’t even notice it anymore except at the height of summer where the A/C also shuts off. The engine is so quite I barely feel the difference when it stops and there is no starter noise when you take your foot off the brake, it’s like hitting pause and resume.
This was a full sized 4WD Ford pickup. It was 100% noticeable.
My Honda CRV will certainly do this*
*If i’m going downhill 
I don’t have enough insight to answer that, but I can believe the other reports that it only goes to 25 MPH. That makes the problem easier of course, with the discharge being closer to 5% than 25%.
I tried to look up the battery chemistry but didn’t find anything. This makes a key difference in how rapidly you can discharge. Usually you can sacrifice some energy density for power density.
I don’t know the cell type, either. They might use cylindrical or pouch cells. Pouch cells have a small maximum distance to the surface compared to cylindrical, so if you put a cooling channel between each one, you can get high cooling rates. The battery is also only operating in pulsed mode, so it can stand a bit of heat just by thermal mass, as long as you cool off between each cycle.
just as a reference point: my smallish e-scooter has a battery of that “size” … 18.6AH x 52v (nominal) = the same ballpark
even 25 mph (40+km/h) seems high to me (assuming close to 2 tons worth of vehicle/driver you have to get up to that speed) - I’d be interested in knowing what voltage this system is, as that of course determines the amp draw …which determines volt. drop and heat/increase of intern. Resistance.
again, just as a reference point my battery is about the size of a shoebox - and I am pretty sure that the Honda battery will have the same ballpark energy density (hence similar size)
I don’t know the specifics but physically, the CRV battery is bigger than that. It’s big enough that it takes up enough room in the back that they don’t provide a spare tire. The ICE CRV still has a spare.