Battery Buying Guide

Start with the system requirement

A battery is one component of a larger energy system. Before comparing products, identify what the battery is expected to do: provide daily energy storage, support selected loads during an outage, shift solar energy for later use, support an off-grid system, or serve another defined purpose.

Then identify the approximate energy capacity and power capability the system needs. The existing Battery Sizing tool can provide an early estimate based on daily electricity use, autonomy, and a usable-capacity assumption.

That estimate is deliberately simple. Actual system design can depend on load profiles, battery chemistry, temperature, inverter losses, reserve requirements, charging limits, cycle-life targets, system voltage, and equipment compatibility.

Compare usable capacity

Battery capacity may be expressed in watt-hours (Wh) or kilowatt-hours (kWh). The headline nominal capacity is not necessarily the amount of energy the system can or should use.

When comparing products, look for the manufacturer's stated usable energy or the conditions and limits that determine it. A battery management system, reserve settings, temperature, discharge limits, system losses, and other factors can affect usable energy.

For an early planning comparison, the site's Battery Sizing tool separates estimated usable storage from nominal capacity. Treat that output as a planning estimate rather than a product specification.

Compare power capability

Energy capacity answers “how much,” while power capability answers “how fast.” A battery can have substantial stored energy and still be unsuitable if it cannot support the required continuous or peak power.

Research continuous discharge capability, peak or surge capability, voltage, current limits, and any manufacturer restrictions on operating conditions or output combinations. In many systems, the inverter or other power electronics also impose limits, so the battery should not be evaluated in isolation.

Consider both the largest individual loads and the combination of loads that may operate at the same time.

Understand battery chemistry

Different battery chemistries can have different characteristics for energy density, weight, temperature behavior, service life, charging requirements, maintenance, cost, and safety considerations. Do not treat chemistry as a simple “best” ranking; its usefulness depends on the application and system requirements.

When a manufacturer identifies a chemistry, research the characteristics that are relevant to the intended use. Look at stated cycle-life conditions, usable-capacity assumptions, charging and discharge limits, temperature requirements, and the manufacturer's installation and safety documentation.

Check system compatibility

A battery that looks good on its own may not work with the rest of the system. Compatibility can involve voltage, current, inverter and charger requirements, communications, battery-management systems, firmware, enclosure or rack arrangements, and approved system combinations.

• What voltage and current range does the battery require?
• Is the intended inverter or charger listed as compatible?
• Are communications or battery-management interfaces required?
• Are there limits on series or parallel configurations?
• Does the manufacturer specify approved combinations, installation arrangements, or accessories?
• Who is responsible for system integration and commissioning?

Do not assume that two products are compatible simply because their basic voltage or capacity numbers appear to match.

Consider installation and environment

Battery performance and installation requirements can depend on temperature, moisture, ventilation, physical location, access, and other environmental conditions. Research the manufacturer's current operating and storage limits before choosing a location or product.

Also consider the practical installation requirements: enclosure or rack space, weight, clearances, wiring, disconnects, protection, access for service, and any requirements for indoor or outdoor installation.

For a tiny home or small-space project, physical constraints can be especially important. A product that fits the energy requirement may still be impractical if the installation location cannot support its weight, clearances, environmental conditions, or service access.

Compare ownership factors

Battery cost should be evaluated over the intended service period rather than only at checkout. Research the conditions behind the manufacturer's warranty and service-life claims.

• Warranty term, coverage, exclusions, and warranty conditions
• Manufacturer-stated cycle life and the conditions used to achieve it
• Usable capacity over the expected operating range
• Service, replacement, and support availability
• Required maintenance or inspections
• Monitoring, firmware, communications, or subscription requirements
• Replacement cost and availability of compatible components
• Shipping, handling, installation, and other ownership costs

Battery comparison checklist

1. Define the battery's role in the overall power system.
2. Estimate required usable energy and identify the desired reserve or autonomy.
3. Identify continuous and peak power requirements.
4. Compare usable capacity and the conditions behind the manufacturer's capacity figures.
5. Compare chemistry and relevant operating characteristics for the actual application.
6. Verify inverter, charger, communications, voltage, current, and configuration compatibility.
7. Check installation location, temperature, moisture, access, weight, clearances, and other environmental requirements.
8. Compare warranty, cycle-life information, service, replacement availability, and total ownership costs.
9. Verify current manufacturer documentation and applicable project requirements before purchase or installation.