What the heat does to a battery
Lithium-ion batteries age faster when they sit hot, through both ordinary calendar aging and the wear of each charge cycle. In a climate where summer overnight lows can stay in the 90s, the pack rarely gets a cool rest, so degradation tends to run somewhat quicker than in a mild coastal city. Most modern EVs fight back with liquid thermal management that cools the pack even while parked, which helps but draws a little energy of its own.
What you notice day to day is range, not chemistry. On a 115 degree afternoon the displayed range drops, partly because heat changes how the battery behaves and partly because the air conditioning is pulling hard. Drivers here adapt in familiar ways: charging to about 80 percent for daily use, parking in shade or a cooler garage when they can, and preconditioning the cabin while still plugged in so the battery, not the drive, pays for the first blast of cold air.
The math on a summer evening
APS and SRP both hit their yearly peak demand on summer late afternoons and evenings, roughly when people get home and the sun is still punishing. Recent summer peaks have run on the order of 7,000 to 8,000 megawatts for each utility at last public report, so the system is already working hard before a single car plugs in. A Level 2 home charger (the 240-volt kind, like a dryer outlet) typically pulls somewhere around 7 to 11 kilowatts, about the draw of several central air conditioners at once.
The saving grace is that EV load is patient. A car sits in the garage for hours but only needs a few of them to refill, so the same energy can land at 11 p.m. instead of 6 p.m. without the driver losing anything. Pushed into the overnight hours, EV charging fills the low valley in demand rather than stacking onto the peak, which is the entire point of time-of-use pricing and managed charging.
Who manages the charge
Both utilities offer price plans built for this. SRP, a public power district governed by an elected board, and APS, whose rates are approved by the Arizona Corporation Commission, each publish time-of-use and EV-oriented plans that make overnight power cheaper than the summer afternoon. Several utilities nationally, Arizona included, have run managed charging pilots where you let the utility nudge your charging to off-peak hours in exchange for a credit, so check the current offerings before assuming any one program is open.
Public charging is filling in too. Arizona's share of the federal highway charging money (the NEVI program) is being used to add fast chargers along corridors like Interstate 10 and Interstate 17, administered by the state Department of Transportation. For renters and condo residents, where a home charger is hardest to install, the slower and less certain piece is multifamily and workplace charging, which is exactly where the programs and the money are still catching up.
Worth watching this month
1. Watch the Arizona Corporation Commission's open meeting agendas for any APS rate or EV program items, most of which are routine but occasionally reset charging credits.
2. Watch SRP board meeting notices for changes to EV price plans, since SRP sets its own rates outside the Commission.
3. Watch for the state Department of Transportation's next round of NEVI charger awards, which decide where fast chargers land on the interstates.
4. Watch the late-season peak demand numbers from APS and SRP as the monsoon winds down, the real test of how close summer came to the limit.
5. Watch the federal Alternative Fuels Data Center for its periodic update to Arizona's registered-EV count, a slow but checkable gauge of how fast the load is growing.