Batteries and power stations have manuals that explain the proper maintenance regime. In my experience, they generally should be recharged monthly and after each use.

My strategy involves the following equipment:

• Several USB battery banks, some that I have and maintain and some that my family members have and may or may not maintain. This includes a few in my domain that are high capacity, including one that has a 120VAC outlet. The cars each have a smaller one with onboard solar recharging cells.
• A mid-size (around 8.5”x11” folded) solar charger that works with any of the USB battery banks.
• Two automotive jumpstarters. Both are full sized and quite capable. When one reached the end of its service life I was able to take it apart and replace its battery successfully, at a much lower cost than that of replacing the whole unit. Sadly, it looks like the manufacturer doesn’t exist any more, and I’m not thrilled with other options I’ve seen so far. Hopefully I can get a few more years out of the units we have.
• A 4000W generator that I’ve maintained carefully, along with 10 gallons of stabilized gasoline that’s rotated regularly.
• Two (and when Eldest Offspring is not at college, three) well-maintained vehicles that can make power, two of them with inverters in emergency kits that are in each.