How much energy can this battery store?
The battery is 60Ah at 16V

So therefore it can provide 60A at 16V for a period of 1 Hour

Alternatively it can provide 30A at 16V for a period of 2 hours

Or 15A for 4 hours - you get the drift.  It's the number of amps it can provide in total when drained flat over a period of one hour.  The slower you drain it the less current you use, the longer it lasts.

So, for 1 hour it's 60A.

If P=VI then P=16*60

That's 960W over the period of 1 hour.

So 0.96KWh.  The length of time this will be for depends on the current you draw.

Your mains power supply has nothing to do with it.