^^This^^ Echo the advice of Daltongang.
There are a few parallel threads related to cars that are spending days between uses. The cars drain the battery slowly on their own, at a rate someplace around 50 milliamps. My normal advice for folks who might leave the car sitting for more than a few days at a time is to invest in a smart battery maintainer, so the battery stays fully charged between drives. Mine sits for days at a time in normal Pilot driving season (winter mostly) since we both work from home. Under the current conditions, it might be two weeks between uses. I have learned to keep a maintainer attached pretty much anytime it's parked these days.
Daltongang's recommendation is to get the battery to full charge before any serious testing. Charging efficiency for the battery isn't even close to 100%, so a battery that's at half charge will take a day or two on most common home battery charger/maintainers. Depends on the charger really, how discharged the battery is, and how the battery is responding to it. Easy maintainers can deliver up to maybe two amps max, which is plenty for maintaining but agonizingly slow when it comes to actually recharging a low battery.
Once the battery charge level is restored, look for charging voltage again at the battery. The voltage regulator function on our pilots is actually managed in the PCM module rather than an onboard regulator that's part of the alternator itself. The PCM regulates charge rate based on more factors than the onboard regulators might, including engine RPM and various temperatures in the engine bay. Pretty smart actually. Bottom line is that it won't try and damage the alternator or the battery when it's recovering a discharged battery. Charge voltage can vary between 13.2 and 14.5, tending towards the higher number under normal conditions.
You can remove the alternator and have it tested at a better parts store. Just know that the tester will need to be able to support the external voltage regulator functions. Before you do that, follow the above guidance and get the battery fully charged before drawing any conclusions.
Tangents:
-- I've settled on the CTEK US7002 maintainer as the weapon of choice for stored vehicles. It has enough capacity to recover discharged batteries in a reasonable time. For most uses, the smaller-capacity units would be fine. CTEK private-labels these for Mercedes and Porsche, and I'm sure for others, so there's a reason to think they are pretty good. Meanwhile, there are plenty of other good units in the market for a fraction of the $110 current cost of the CTEK I like. Today's Amazon Deals has a decent unit for around $35, and the local Costco usually has something in the $30-40 range on the shelf.
-- My annual electrical maintenance routine includes some predictive testing, looking at the specific-gravity of the fluid (acid) in the battery. Testers are under $5 at the parts store. Gloves and glasses since the fluid is acid, but you get a good idea of the remaining battery life. The battery does need to be fully charged to test. When you start to see balls in the little tester that don't float, you know to go battery shopping before you actually get stranded.
-- I haven't yet jumped on the portable jump-start booster units yet, but may. Plenty of options, including units that have USB ports to keep your phone charged in an emergency. I'd need to find a place to keep it connected/charged, and out of the way. I don't have things loose in the car, so would likely end up with a pigtail wired into the trailer wiring circuits so I could hide the unit in that rear left cubby, along with the portable air compressor and the trailer hitch parts and heavy-duty flashlight already secured there.