Choosing a battery-how to pick the best solar battery for you
When comparing quotes for different solar battery systems, it can be difficult to determine which characteristics and technical specifications matter most and with good reason: the home energy storage industry is so new that you probably don’t know anybody with a battery who you can ask about their experience. While every battery has to meet certain reliability and safety requirements in order to be sold and installed in the US, outside of those standards there is very little standardization of specs and characteristics across the batteries available on the market today. We’ve provided some tips on what to look for when comparing different battery quotes.
What to look for in a home solar battery: six measurements to consider
A solar battery stores electricity for later use, so you can keep appliances running during a power outage, use more of the solar energy you produce at your home, and even save money on electricity in some cases. They are often referred to as "deep cycle batteries", due to their ability to charge and discharge a significant amount of electricity compared to something like a car battery.
Energy storage systems provide a number of different benefits, from emergency backup power to even financial savings. But they also bring technical complexity and a new set of unfamiliar terminology. Here’s what to focus on and look for in a deep cycle solar battery: 

How to decide which battery specs matter for your needs
There are a number of different potential decision criteria and comparison points to make when evaluating your energy storage options. Here are a few of the most common decision criteria, as well as which battery specs matter most if these criteria match your situation:  
1. If you want to power more of your home at once, look for a solar battery with a high power rating
2. If you want to be able to power a more energy-intensive appliance (like a sump pump), look for a battery with a high instantaneous power rating
3. If you want to run your home with your solar battery for a longer amount of time, look for a battery with a higher usable capacity
4. If you want to get the most out of every kilowatt-hour of electricity you put into your battery, look for batteries with a higher round trip efficiency 
5.If you are space constrained and want to get the most amount of storage out of the least amount of space, look for lithium-ion nickel manganese cobalt (NMC) solar batteries
6.If you want a battery with the longest lifetime that you can cycle the most amount of times, look for lithium iron phosphate (LFP) batteries
7. If you want a battery with the absolute highest safety rating possible (don’t worry, they’re all safe!), look to LFP solar batteries

The power rating of a battery refers to the kilowatts (kW) of power that the battery can provide at once. In other words, a battery’s power rating tells you both how many appliances your battery can power at once and which appliances those are. 
Power is expressed either in kilowatts (thousands of Watts) or in Amps, and different appliances use different amounts of power. For instance, a typical compact fluorescent lightbulb will use 12 Watts (or 0.012 kW) of power, while a 3-ton AC unit will draw 20 Amps, which is equivalent to 4.8 kW. Most of the batteries available on the market today have a continuous power output of around 5 kW. 
Importantly, solar batteries often have two different power ratings–a continuous power rating and a 5-minute or instantaneous power rating–meaning they can provide more power in short bursts. This is important if you have an appliance like a sump pump that requires a large amount of power to turn on, but then runs at lower power.
A battery’s capacity (or size) is the amount of electricity that a battery is able to store and supply to your home. While power is expressed in kW, battery size is expressed in kilowatt-hours (kWh), which is power multiplied by time. As a result, a battery’s storage capacity tells you how long your battery can power parts of your home. Be sure to look for the usable capacity of a battery, as that number represents the amount of stored electricity that you can actually access in a battery.
Since electricity usage is power multiplied by time, if you are using more power, then you’ll run out of stored electricity faster. Conversely, if you’re only using your battery to backup a few appliances with relatively small power consumption, you can keep them running for a longer amount of time. This makes the size of a battery slightly misleading, because the length of time a battery's charge will last is directly influenced by how much power it's outputting.
Think about the example above of the difference between a light bulb and an AC unit. If you have a 5 kW, 10 kWh battery, you can only run your AC unit for two hours (4.8 kW * 2 hours = 9.6 kWh). However, that same battery would be able to keep 20 light bulbs on for 2 full days (0.012 kW * 20 light bulbs * 42 hours = 10 kWh).