I need help with this XLE issue

[The Little Prince]

I've been helping my neighbor with his 2020 Highlander XLE that's been acting weird electrically speaking LOL. There's already a new AGM battery that went in a few weeks ago, and we added a dash voltage readout, too. At idle or rolling downhill, it holds steady around 14.4V, but the moment you're on the gas, it drops to about 12.4V and doesn't recover until you lift off. Is this pointing to a weak alternator, or is Toyota's charging system just set up this way? I would like to know the right way to diagnose it before he spends more money at unnecessary parts.

 

[HighlandCrawler]

I'm not an expert, but when you see a voltage drop while the system is under load, I think it usually points to either a weak alternator or some bad connections. It's a good idea to check the alternator's output at a specific RPM using a multimeter. Generally, you want to see at least 13.5 volts while the system is under load. Hopefully, an expert will weigh in on this too