I’m looking a battery for use with solar power and it has the following specs.

Volts 12
Capacity @ 20-hr rate 120
Capacity @ 100-hr rate 145

How does this translate into running a 1000 watt appliance and how long you can run it with this battery.

Best answer:

Answer by campbelp2002
Watts = Volts * Amps.
So a 12 volt battery supplying 10 Amps is producing 120 Watts of power.
Batteries are rated in Amp-Hours. For example one battery might be rated at 100 Amp-Hours. That would mean it could supply 1 Amp for 100 hours or 2 Amps for 50 hours. But it could probably not supply 100 Amps for 1 hour. Batteries work better at low rates of use. Your examples are 20 hour rate gives 120 Amp-Hours, meaning it can supply 6 Amps for 20 hours (6 Amps times 20 hours = 120 Amp-Hours), but if you drain it more slowly, taking 100 hours instead of 20, it will give you 145 Amp-Hours, which would be 1.45 Amps for 100 hours.

To get Watt-Hours, multiply by the number of volts. Most such batteries are 12 volt (but not all are so check). So a 12 volt battery that has a 120 Amp Hour capacity has a 12 * 120 = 1,440 Watt-Hour capacity. Since one kilowatt (kW) is 1,000 Watts, that would be a 1.44 kilowatt-Hour (kWh) battery. You electric bill is usually in units of kWh. Check your electric bill to see how many kWh a month you use, then divide by 30 to get the number per day. That will give you an idea of how many batteries you need to store enough energy to make it through the night if you are off grid and relying on solar panels for all your power. I suspect you will be shocked at the number of batteries needed.

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