4 Storage technologies

[Skvez]

I can't think of more than 4 ways to store (Electric) Power:

1] Capacitor.
Stores electrical energy (DC) directly
Very small quantities compared to other storage options
High efficiency
Suffers from Leakage proportional to size (small caps have small leakage, big caps have big leakage)
Life expectancy of decades

2] Battery
Stores electrical energy by converting it to chemical
Moderate storage capability compared to other storage options
Moderate efficiency
Suffers from self discharge
Life expectance of years

3] Spinning Mass (flywheel)
Stores electrical energy by spinning a flywheel (often in a vacuum to reduce frictional losses)
Moderate storage capability compared to other storage options
Moderate efficiency
Suffers from frictional losses in bearings
Life expectance of years (in particular bearings wear away)

4] Potential energy (pumped storage)
Stores electrical energy by moving a mass (often water) 'up' and using this potential energy at a later date to drive a generator
Large storage capability compared to other storage options
Very Poor initial inefficient
Once the mass us 'up' ongoing losses are minimal.
Life expectancy of years (generators require replaced).

For us '3' and '4' are uncommon. '1' doesn't provide the quantity of energy we need except perhaps for small solar->light applicatons so most of us are stuck with '2' batteries.
I worry about what we will do in a TEOTWAWKI scenario after 10 or 20 years when the batteries all fail.