Selecting the Right Batteries for Off-Grid Energy Storage

Before you choose batteries, you need to know your energy usage. Look at how many watt-hours you use daily (not just peak wattage). A kill-a-watt meter or whole-home energy monitor can help you get a solid baseline. Or, to get an estimate without a meter you can use generic power consumptions shown on the energy.gov website:https://www.energy.gov/energysaver/estimating-appliance-and-home-electronic-energy-use Multiply your daily energy use by the number of days you want backup for, and you’ve got your required battery capacity.

Example: If you use 5,000 watt-hours a day and want 3 days of backup, you’ll need 15,000 watt-hours (or 15 kWh) of battery storage—before considering depth of discharge.

Know Your Battery Types

There are three main types of batteries commonly used in off-grid systems:

1. Flooded Lead-Acid (FLA)

• Pros: Cheapest upfront, well-known technology, recyclable.

• Cons: Require regular maintenance (watering), must be vented due to off-gassing, shorter lifespan (3–5 years).

• Best for: Tinkerers who want low cost and aren’t afraid to get their hands dirty.

2. Sealed Lead-Acid (AGM & Gel)

• Pros: Maintenance-free, safer to store indoors, more tolerant of cold.

• Cons: Higher cost per cycle than FLA, still heavy and bulky, shorter lifespan than lithium.

• Best for: Users who want simplicity without the maintenance of FLAs.

3. Lithium Iron Phosphate (LiFePO₄)

• Pros: Long lifespan (10+ years), high efficiency, deep depth of discharge (80–100%), lightweight, compact.

• Cons: Higher upfront cost, needs a battery management system (BMS), sensitive to extreme temperatures.

• Best for: Those looking for long-term, hands-off performance and can afford the initial investment.

Depth of Discharge (DoD) and Battery Sizing

Batteries don’t like being drained completely. Lead-acid batteries should only be discharged to about 50% regularly, while lithium batteries can safely go down to 80–100% DoD. That means you’ll need more amp-hours in lead-acid batteries to achieve the same usable energy as lithium.

Using our 15 kWh example:

Lead-acid (50% DoD): Need 30 kWh of storage.

Lithium (90% DoD): Need ~16.7 kWh of storage.

Battery Voltage: 12V, 24V, or 48V?

Higher-voltage systems are more efficient. For systems over 2 kW, 24V or 48V is recommended to reduce current, wiring size, and energy loss. 48V is ideal for larger setups, especially if you’re running heavy loads like well pumps or power tools.

Temperature Matters

Batteries hate extremes. Lead-acid loses capacity in the cold, lithium shuts down if it drops below freezing while charging. If your battery bank is in an unheated shed or garage, either insulate and heat it or choose a battery chemistry more tolerant of temperature swings.

Maintenance and Monitoring

All battery types benefit from monitoring. A good battery monitor (like a Victron BMV or a smart BMS) helps you track charge, discharge, and overall health. For lead-acid, plan monthly maintenance; for lithium, let the BMS do its thing and check it once in a while—kind of like your brother-in-law with his backyard smoker. 😄

Download our free google spreadsheet template to help you calculate power usage and the number of batteries and solar panels needed. You can get it for free here: Solar Panel & Battery Calculator