One, water leaks. I had an 08 XC70 I recently worked on that had a leaking windshield seal, water was getting down to the CEM under passenger side dash and causing similar symptoms. A clogged sunroof drain can also allow water to to leak into cabin and can cause multiple electronic issues. Parking under trees is the main culprit of water leaks into cabin. Given you said a storm came through and then you experienced electrical issues would make me look for a water leak into cabin. When checking the the windshield seal, apply moderate pressure near upper corners of windshield and look for movement. You can look for clogged sunroof drains by moving the sunroof back and examining for either debris or water in the sunroof tray. There are two front holes, one on each side that typically clog. Examine from outside looking down into tray edges, a small light will help. If the tray looks clean with zero signs of plant debris, I always poor a small amount of water into front tray on either side, maybe 4 to 8 ounces, and look to see if it drains properly onto the ground, right behind front wheel area. If it doesn’t drain out the hose may be clogged internally with debris. Look for any water leaking into cabin at this point, look around headliner and interior trim that runs down the windshield, pull back carpeting from under dash and check for wetness and or leaks or signs of leaks. Passenger side leak would be near the CEM. In some cases , the sunroof drain tubing over time shrinks and can pull out of grommets and cause the leak into cabin. If its not leaking into car or draining from the tray, hose is likely clogged. I would then use a small thin metal cable, like a bicycle cable but even thinner, to run down from the corner of the tray in an attempt to dislodge clog. Avoid using compressed air in this situation as if the clog is significant, it can pop the hose out the grommet behind the dash and its very difficult to reattach if that happens, sometime windshield removal is necessary if that happens. Some clogs I have had success with using a syringe filled with Roto-Rooter and squirting a few cc’s down the drain hole. It takes a few minutes but usually dissolves the clog. Syringe I use is the type for administering liquid antibiotics, such as children’s amoxicillin, usually a 10cc plastic syringe from the pharmacy. The roto-rooter method has to be done with extreme caution as its a very caustic chemical and will cause bleaching, staining and corrosion it not used properly. Place something under where the fluid would hen drain out once leak is disolved, otherwise it will stain concrete floors, I use plastic trash can lids when using this method. Never use this method first without verifying there is no other leak from drain hoses into cabin. You really don’t want that chemical getting on much inside, such as electronics and carpeting.
Two, battery cables. Positive cable incorporates a large inline fuse that is not replaceable. I’ve seen many that go bad intermittently caused by corrosion. Some will make contact again when moved or jiggled. A simple voltage drop test of the positive cable would confirm. Sometimes you can even see the swelling of the cable in areas due to the internal corrosion of the copper cabling. Replacement cables are available. Short of that, the bad section can be cut out and a cable repair can be done it you have the proper tools for that.
Sounds to me you could have one of those issues if not both.
If neither of those apply, a simple closed current battery draw test would be a good idea to see if there are any battery draws. When vehicle is locked and all modules are in sleep mode, current draw should be under 30 milliamps. Anything over that would indicate a higher than normal current draw and offending module or system tracked down. RDAR units, in the audio system are known culprits for battery draws. Its the Digital Receiver for Satellite Radio, many are not used but module likes to fail and cause unexpected overnight drain on battery.
Hope this helps diagnosis.