We don’t know the history of the vehicle and batteries are *routinely* problematic.
1. test for a drain in the vehicle. It’s a simple test.
2. have the battery tested at any major national chain like advanced auto parts, etc.
more than likely the battery is weak and the first time it ran low degraded it and it’s now junk.
again we don’t know the history or how likely options 1 and 2 are
Get a better battery and never think about it again. Get something with more power then the stock unit. Get an Odyssey if you want the best, call them and ask which one.
The battery might be bad or the first time it died degraded its capabilities. They are *not* forgiving.
Youre over thinking it. More than likely the first time it ran low was more than a week - and was preceded and/or proceeded by short trips where the battery wasn’t fully charged.
Batteries degrade every time they run low - so you’re making it worse every time it does this.
You could check for a drain and/or have the battery tested.
What a mess, with the crap on the front of the cover, I'd say it's coming from higher up. Front main seal, probably.
Clean that thing off. You'll never pinpoint it with dirt and oil everywhere like that. Get a can or 2 of engine cleaner, grab a pair of ramps, and head to a coin-op car wash.
Hard to say. If they’re rebooted with Subaru boots they can last. Only takes one or two Subaru OEM reboots to make 300k. But cheap axles are so common there’s no way to say.