In terms of long term battery function and capacity, is there any advantage to running the battery down vs. topping up frequently? I've heard this is true about rechargeable batteries in some applications, but I haven't seen anything with regard to the PIP battery.
Its best to charge just before use. I have my timer set to finish charging at 5 AM. I only recharge during the day if I'm going to use the charge before the end of the day. I understand leaving the battery at full charge (which is actually 85%) during very hot times should be avoided. I consider "avoided" to mean if convenient
Thanks, CBear, that's helpful. Since posting, I've found some more information relating to the specifics of the Prius's Li-ion battery and charge-recharge cycle. Apparently, until recently it was thought there was no memory effect in Li-ion batteries, so you could charge whenever you liked. Now, however, that's changed. Recently it's been determined there is some degree (how much, I don't know) of memory effect in Li-ion batteries (verified by Toyota, according to one source), so you might think it would be better to charge and discharge fully rather than keeping the battery topped up. BUT, it turns out the main body of charging and discharging the battery in a PIP actually takes place during driving, and switches back and forth constantly. Therefore, most of the charging and discharging is outside your control, so what you do with actual plug-in time may turn out to be virtually irrelevant. (I have not seen anyone commenting on this specific point. It just seems likely to me from other information.) Please, dear readers, keep in mind that what you're now reading is based on a half-hour review of what's available online. I hope it's accurate, and I did try to use reliable sources, but if anyone out there knows more about this, please feel free to correct any of the above.
i won't say it's inaccurate, but it's all news to me. what do you mean by 'the main body of charge and discharge takes place while driving'? that's all controlled by computer, and not left to chance. whereas, when you charge the battery, you control quite a few variables. that being said, i have never read or heard that topping off the pip battery is a potential problem, so i do it all the time.
I think a minor memory effect in Lithium Ion batteries has been detected and reported recently. The fact that they just noticed this tells you that the effect is so minor that you don't need to think about it unless you are a scientist working on battery chemistry. As far as topping off, I wouldn't worry about it unless temperatures are hot and then it might worth considering. Even at 85% full there will be some significant additional degradation from hot temperatures. It's worth parking in the shade, when possible, during the summer.
Allowing the battery to rest (known as a "cold soak") prior to recharging is helpful. Since evening electricity rates are lower anyway, that's a win-win situation. The timer makes that quite convenient too. Just hit the button and plug in before you leave the car for the evening. As for running it down to "empty", the system prevents the battery-pack from hitting the common lows you see in portable devices. The assumption that 0% is fully depleted is quite common. What actually happens is the engine fires up, switching from EV to HV mode automatically, when the charge-level drops to 23.5%. That helps with longevity. Another approach to slow the aging process is never fully recharging. The system automatically stops at 85%. Staying well away from 100% capacity is known to be quite beneficial, something we don't take a second thought about with other rechargeable devices. Not allowing that with Prius is how the design avoids ever needing battery replacement. With respect to system "switching back & forth", that type of HV energy activity is just shallow touching of the battery-pack. Being just a tiny fraction of the electricity transfer during plug-in recharging and sustained EV draw, you can still have a big influence. You can choose when to recharge and push the EV/HV button. Thanks for starting this thread. It's nice to see some back-to-the-basic questions being asked.
The only way you may see this memory effect is if you've never plugged it in, then suddenly after about 3 years bought a house with a garage and then decided to plug the car in. You may not realize the maximum charge until a few plug-in cycles. iPad ? HD
I think we will only know this for certain after we see a ton of numbers showing how hot the battery is actually getting in comparison to driving.
After much research, it's clear to me that lithium batteries don't like to be discharged too deeply. Neither do they like to be fully charged. The best longevity can be obtained by topping up frequently, but not to 100% charge. I believe the Plug-in Prius takes care of this by showing a full charge at 90% of battery capacity. Also, when the battery registers as depleted, it still has at least 50% charge remaining overall. Because there is a "virtual partition" between the plug-in battery and the hybrid/regen battery, there's always enough left in reserve to protect the battery and to maintain hybrid operation. As mentioned elsewhere, the ICE/generator kicks in automatically whenever the battery is in danger of being discharged too much. I'm sure someone will correct me if I have some of the details wrong. I believe the nickel metal hydride batteries used in the regular Prius are more forgiving of deeper charge/discharge cycles, and indeed they require it periodically to deal with a partial "memory effect." Also, the NiMH cells tend to be harder to equalize, and frequent cycling helps this somewhat. For my money, the modest gain I get from plugging in, is offset by the deterioration of the lithium battery pack. I tend to keep it charged and only use it when I want to "run silent."
For what it's worth, the only time I get the maximum EV range to show after a charge, is when the vehicle has either been in a heated garage, or after a warm spell of a few days. The rest of the time I'm getting somewhat less range.
The NiMH battery used in the regular Prius is usually kept in a narrower charge range of around 40-60%, I think, although they sometimes go outside that range going up and down steep road grades etc. The memory effect you are thinking of applies to the older NiCd chemistry batteries, not NiMH.
Probably the wall charge is always going to depend upon universal differences, such as driver, location, temperature, etc. Right now I am consistently getting 16.1 to 16.4 EV miles charged overnight in an unheated garage during cool Maine nights. I've been trying to take note of actual mileage driven on a charge and it is common to run 15.5 to 15.8 miles going no faster than 40 mph. I wouldn't be able to do that at higher speed.
