Does hot weather affect battery performance?

One very important element of keeping reasonable battery life is making sure the charging profile is temperature compensated. Which means the charger needs a way of measuring battery case temperature with some reasonable accuracy.
typical float voltage for a flooded lead acid is about 13.6V @ 20C (room temp) but decreases 30m/C so at 40 C (100f) it is down to 13.0V, at 50C (122f) around 12.6

Same thing for bulk charge rates

So a charger that doesn't account for battery temp will be overcharging a battery at high temperatures.

if the battery is just sitting not being charged a few weeks, even a month or so of high temps isn't going to do much if any damage or reduce life significantly. Long term high temps then battery life goes down no matter what you do about charging. One of those things than helps us stay alive, most chemical reactions have a positive temperature coefficient.

Lead acid batteries perform better in warm weather but hot weather shortens their life. You can’t regulate air temperature but to can shade the battery box from direct sunlight.

Per Trojan…”For every 18° F (10° C) rise above room temperature (77° F or 25° C), battery life decreases by 50%. Charge your batteries fully after each period of use. Allowing your batteries to sit in a low state of charge for extended periods will decrease their capacity and life.”

https://www.trojanbattery.com/tech-support/battery-maintenance/

mr_andyj wrote:

Extreme heat speeds up the chemical reaction inside a battery and causes an increase in the self-discharge and plate corrosion. This leads to sulfation which can cause irreparable damage to the battery.

For each 10°F rise in temperature, the life of a sealed lead acid battery is cut in half. Therefore, if a battery in a stationary position that should last for 4 years at normal temps, would last 2 years if exposed 92°F and even less if exposed to typical desert temps of 106°F.

And of course, this is talking about long term effects.

I help out our Kuwait office and 7 months of the year triple digit temps are normal. Mid summer 120-125F (actual temp not feels like) are not uncommon. The guys I work with tell me 2yrs out of a starting battery is doing good.

Assuming the OP is talking about the heat wave in the NW that is likely to last only a week or so, it's unlikely to have a measurable effect.

Look no further than your car/truck for that answer. A car battery in Phoenix Arizona lasts 2 years. A car battery in San Francisco lats 5-7 years. A car battery in Buffalo NY lasts 4 years. Heat kills a battery faster than anything.

Good topic, as I have never thought of it. I keep my batts inside the coach where it is a more stable climate, except for that it is vented and sealed air tight from the coach.

Do you even have the option to move your batts to a cooler location?

There is a little thing called "internet search engines" . One in specific called "Internet for DUMMIES" is called Google. There are other good and safer search engines out there, lol, just kidding.

Within seconds I found this article:

As the weather heats up, you need your summer toys and equipment to push through high temperatures without worrying about the reliability of your lead batteries.

Many batteries perform at a wide range of temperatures; when extreme temperatures come into play you need a reliable battery – and to follow proven charging and storage best practices. Here are some battery maintenance tips to keep your batteries performing in extreme temperatures.

STORAGE AND USE
Extreme heat speeds up the chemical reaction inside a battery and causes an increase in the self-discharge and plate corrosion. This leads to sulfation which can cause irreparable damage to the battery.

For each 10°F rise in temperature, the life of a sealed lead acid battery is cut in half. Therefore, if a battery in a stationary position that should last for 4 years at normal temps, would last 2 years if exposed 92°F and even less if exposed to typical desert temps of 106°F.

In some areas, heat is unavoidable. If this is the case, be sure to store batteries in either a climate controlled space, or under the shade of a garage or parking cover. Once a battery is damaged by heat, it cannot be repaired.

CHARGING
Batteries can operate over a large temperature range, but when it comes to charging, you need to be careful. Charging temperatures are limited and, for best results, most batteries should be charged between 50°F and 86°F.

To avoid the hazards of heat or cold, the best practice is to let your battery come to room temperature before charging. If you’re not sure which battery can withstand the temperatures of your climate, flooded lead acid batteries are one of the most reliable systems and are well suited for hot climates. With proper maintenance, these batteries can last for many years of reliable service.

Good quality lead batteries perform reliably when exposed to extreme environments and have a wide operating temperature, ranging from -40°F to 120°F. Lead batteries are also more forgiving when subjected to temperature extremes.

For extreme temperatures, it may be best to install batteries that are purpose-built for difficult applications. Crown Battery’s Severe Duty Batteries perform where other batteries stop. Crown’s advanced technology has combined the essential characteristics of a high-performance battery – with the endurance features you’ve come to expect from Crown – into one incredibly tough battery that is like no other. In applications where many products fail due to extreme temperatures, maintenance charging or duty cycle – Crown’s Severe Duty Batteries deliver reliability.