At this time of year we think more about the cold and it's affect on batteries. Anyone who has used old lead acid batteries knows they are very poor in the cold. Some blame lower gas mileage on the cold but isn't it many other winter factors. How do NiMH and lithium batteries compare to old lead acid in the cold. I know my 2005 prius will not go into idle stop as quickly until the ICE engine gets warm. If I turn off the heat it will stop almost at the same time I turn it off. When to run the deprost it also used the dehumidifying of the air conditioner so that adds more load. Cold tires are also softer and have more rolling resistance. There are simply a lot of factors. Also be sure to compare the mpg of a plain ICE car in the cold. If they had good displays like the prius many would be ashamed. Add your stories here and let us know what you experience.
The effect on mileage due to cold is very little related to battery efficiency. The real culprit is the ICE. The ICE only runs efficiently when it is warm, and won't shut off until it is warm. If you are driving with an unblocked grill, with heat/defrost on the engine may NEVER get warm if you don't block the grill. Simple grill block can and 5 mpg instantly! Other factors are tire pressure, winter formulated fuels, snow, slush, rain etc. I can still get ~50 with temps in the 20's, with the grill 90% blocked. It still takes 15+ miles for the ICE to get to 185f, the point where the t-stat BEGINS to open. Icarus PS Battery capacity goes down with temperature, but battery life goes up.
A bit of theory. Killer on NiMH batteries is heat and not cold. Both charging and discharging heat up the battery. Higher the electrical current, more resistance there is and more heat is being produced inside battery. A bit of practice. When very cold, my Prius likes to charge the battery much more than during summer heat. That would coincide with theory. Regarding heating our asses during winter, well, as there is no decent (read as at least 2 kW) electric heater built in, well the only way to warm up the cabin is through inefficiency of internal combustion engine called heat. Colder it gets, more time ICE needs to warm up both itself and then occupants inside the car. This details make some interesting consequences - pure electric or plugin hybrids should have electricaly powered heat system built in if the cars will be sold for use in colder climates.
There is a roughly parallel discussion going on after post #50 in this thread: http://priuschat.com/forums/fuel-economy/53689-short-trips-heres-trick-7.html Perhaps the posters here would come over and offer your thoughts. Thanks. Before you go, I'd like to ask, Ogo, you said: "When very cold, my Prius likes to charge the battery much more than during summer heat." Elsewhere it has been noted that in cold temps you often see more "green bars" than when its warm. Could this be the HSD CPUs charging the HV battery to a higher level, using the charge, and recharging as a way to maintain optimum internal HV battery temps? What is the HV battery temp range for optimum performance -- and I presume optimum longevity?
In the solar world we use a temperature of ~77f/25c as a reference datum. Above that battery output goes up, longevity goes down. Below that the inverse. Remember, as the battery charges and discharges it creates it's own heat, so while it may be cold outside, after a number of miles, the cabin warms up, the battery warms up due to both the cabin being warmer and it's own internal heating. I suspect that if you were to do a real world test over some given number of miles you would find almost no difference that is attributed to cold batteries. If you want good mileage,,,block your grill! Icarus
So...if you block the grille, and it interferes with warming the engine, what does that do to the life of the ICE?
Lithium is known to work over a very large temperature range. although not as a bad as lead, afaik, older NiMH is affected by temperature, the newer technology can go as low -30 and as high as 70 C but only for charge storage... efficiency per se, should not be different. ScienceDirect - Journal of Power Sources : Recent advances in NiMH battery technology
It doesn't interfere with the warming of the engine it is helping with the warming of the engine. Arguably, you will be adding to the life of the engine, because the wear curve on engines goes way up as the temp of the engine goes down. The ICE is designed to run ~200f. Below that it is running at a very inefficient temp. The car is designed to run at all temps and not over heat (Mojave in June for example) and as such trade offs have been made. For years we used to put cardboard in front of the radiators of our cars, and even now most highway tractors have shutters in the grill and winter fronts to keep the engine heat in. Blocking the grill does essentially the same thing. Using a scan gauge confirms that the engine will never get truly warm in very cold weather with the grill unblocked. It also confirms that blocking the grill in COOL weather will not result in overheating. Above ~65f I take a piece or two out, but even at 85f I still block part of the grill and have never seen coolant temps above 210f. Icarus PS Somewhere it was suggested that 90% of all engine wear occurs in the first 5 minutes of operation. This is due in some part to rich mixture (largely cured with good fuel injection), poor lube oil circulation due to cold oil, internal engine parts wearing because they haven't expanded to their design size, allowing blow by, acidification of oil etc.
That's only true for modest winter temperatures. Much colder, like Minnesota, the benefit drops to mostly just a hot heater. .
I'd put a lot down to rolling resistance on wet and slushy roads. I drove 120km on dirt roads earlier in the week and had terrible mileage, 7.0L/100km @ 110km/h. On sealed roads at the same speed I was getting 5.2L/100km with a cross wind.
What I've gleaned from others is that it is supposedly safe to do both as long as temps don't exceed 60 F. However, without a Scangauge this is running blind (I don't have one at present.) It's my understanding that some fans will kick on if something gets too warm. Since I've never heard any of them, come on it appears that I've not pushed anything too far. Top grill blocking should be safe regardless according to others I've read (although I would remove it in summer) so I did it first. Adding the bottom grill blocking when temps will stay below 60 is what I've picked up from others. Some do total blocks of the bottom grill, I blocked 4 of 5 lower grill slots. In doing so my ambient air temp. indication from the lower grill still appears to be reasonably accurate, and I know there is some circulation. I expect to begin removing some of the blocking around March 1.
