Heat and battery life

I'd actually like to see the answers for this question too. The summer temps here are usually between 100-115 degrees and I usually notice the same thing. The battery draining at a faster rate has to be due to the heat. I have noticed that if I kick my air up a few notches to keep the battery cool that usually helps a bit. I'd love to hear some answers from the pros though.

 

I agree it must have a lot to do with the battery's "comfort" level and not being happy when its real hot...like me!

 

Are you using the AC immediately? I've seen the same thing if I turn the AC on right away. During the first warmup stage (~1 minute) the car prefers electricity for propulsion. The AC, also pulling from the battery, will be working its hardest when first turned on in a hot car. Add those factors to the stop and go traffic I often see pulling out of the lot, and it's easy for me to drop it down to 1 or 2 bars -- and run the ICE while sitting in traffic . So I generally try to tolerate the heat for a few minutes, waiting until I can run at a more sustained pace before I turn the AC on.

Can-View generally shows the battery temp to be below 100F when I first start, with it gradually heating up from there if I don't run the AC on a hot day. I can't remember the critical temperature threshold at which battery performance starts to suffer -- I think it's in the neighborhood of 104 or 105. Others more educated than I can verify.

 

The answer is simple, sort of.

First, the battery capacity is not changed very much by higher temps. The battery will not loose charge from the temp directly, just may not charge at high current. The system will notice the higher temp of the battery and try to protect it by reducing high currents into or out of the battery, to try not to heat it further, all the while trying to maintain at least 40% SOC (zero to two bars on meter or thereabouts).

Second, the A/C runs off the high voltage system. This can mean the battery, but also the generator output (indirectly, the HSD electronics directly). In the case of a hot battery most of the power for the A/C will come from the generator, which could reduce charging current. This would be a "good thing" because charging will heat up the battery further. It would also not be a problem, because the HSD system would be trying to keep the charge current down until the battery temp came down. It does mean the ICE will be inclined to run most of the time (controlled by the HSD system - the ICE doesn't have any desires of its' own).

Generally, because of the above, if it's really hot out you will notice lower SOC for the battery, unless you descend a very long hill (5 min or longer), in which case the system can charge the battery and run the A/C, all the while keeping temps under control. Also, once the A/C has cooled the car interior, the battery can be safely brought back up to "normal" SOC levels, as its' cooling air comes from the cabin air.

100 F isn't "too hot" for the battery BTW. I would expect 50C (122F) to be the control point, or around there. Because the battery is "buried" in the bottom of the car, it wouldn't reach the car's interior temp. It -would- reach the outside temp and would heat up rapidly from that under use.

I presume the battery fan was running most of the time?

 

<div class='quotetop'>QUOTE(JimboK @ Aug 7 2007, 10:05 AM) [snapback]491795[/snapback]</div>

I've seen the same thing. The A/C pulls a tremendous amount of power and the battery can't keep up all by itself for more than a few minutes. My technique on hot afternoons is to keep the A/C off and windows down while I roll through the parking lot, taking it really easy until the ICE warm enough to do the pulling. (At 100F that's well before I reach the street.) I accelerate directly onto a main road, so I get up to speed and then engage the A/C once cruising. That way the ICE takes the load and the battery can just hang out. SoC stays right up at 6 bars when I do this.