Devices to store off-peak (cheap) electricity for on-peak use

My water boiler has a feature which allows it to heat overnight when electricity is cheap, and it got me thinking that it would be a great money-saver (and stealth) way of doing things with respect to growing.

However, I'm not very knowledgeable of electric power storage units, so perhaps they either already exist, or aren't feasible.

Is there something out there which can draw power from the mains at off-peak hours, and then have devices plugged in to make use of that throughout the rest of the day? Is this a reasonable request or is there something massively flawed in my logic?

I dont see why you cant hook up 12, 12 volt batteries in series amounting to 120 volts and charge them during the off peak hours and run you stuff of them during the day.

This is an interesting thought. But buying *10 deep cycle batteries doesnt sound like a way of saving money IMO. Especially good ones like golf cart batteries. Im sure theres some other commercial scale capacitors that you could get ur hands on, but Its also a risk of fire (lots of heat). Not to mention it takes more power to charge a battery or cap than the output it gives back. But I guess if its cheaper than peak hrs it could possibly save money in the long run.