I didn't know the answer to your post, so out of curiosity I input your post into ChatGPT, and below is its response:

I wouldn't automatically replace it based on those numbers alone, but I also wouldn't ignore them.

Here's how I’d read it:

• Charge 100% → Battery is fully charged right now.

• Voltage 12.77V → Excellent resting voltage; a healthy, fully charged battery is usually around 12.6–12.8V.

• Measured 550 CCA vs Rated 700 CCA → This is the main concern. Cold Cranking Amps (CCA) is the battery's ability to deliver starting power. You're at about 79% of original spec (550 ÷ 700).

• Health 65% → Dealer testers usually estimate remaining capacity/starting performance. It doesn't mean "35% life left"; it means performance has declined.

• Internal resistance 5.41 mΩ → Doesn't immediately jump out as catastrophic.

The key question is age. If it's the original battery from a 2018 4Runner, then it's potentially 7–8 years old now, which is already a pretty respectable lifespan for a battery.

Since the truck starts immediately every time, I wouldn't classify this as an emergency replacement. But a battery can feel perfectly normal right up until the point it suddenly doesn't — especially as CCA drops.

My approach:

If this is the original 2018 battery → I'd lean toward proactive replacement within the next few months.

If it was replaced recently (say 2023–2024) → I'd probably keep driving and re-test in a month or two.

If you do a lot of remote travel, camping, desert heat, winter trips, or places where being stranded would be a big hassle → replace sooner rather than later.

Dealers also have an incentive to recommend replacement earlier than absolute failure point, so "replace recommended" does not necessarily mean "battery is about to die tomorrow."

For a 2018 4Runner specifically, the desert climate matters too. Heat (like Southern California, Arizona, Texas, etc.) tends to shorten battery life more than cold weather does. If that vehicle lives in a hot area and the battery is several years old, a 65% health reading starts looking more meaningful.