Solar batteries: lithium (LiFePO4) or lead-acid, how to choose

For a backup or solar system, lithium LiFePO4 batteries generally offer more usable capacity, more cycles and less maintenance. Lead-acid batteries (AGM, gel or flooded) usually need a lower upfront investment, but they wear out sooner if deeply discharged and cope less well with heat. The right choice depends on how you use them, where they will be installed and your budget. This guide helps you compare before choosing an inverter and batteries in Las Terrenas.

Battery types

Lithium iron phosphate (LiFePO4)

This is one of the most widely used chemistries for home solar storage today, and one of the lithium chemistries considered most stable under heat. Each battery has a management system, the BMS (Battery Management System), which protects it against overcharging, excessive discharge, out-of-range temperatures and cell imbalance.

• A large share of its capacity is usable.
• Practically no routine maintenance beyond monitoring.
• Must be compatible with the inverter, which often communicates with the BMS.

Lead-acid

• Flooded: the electrolyte is liquid. Its level must be checked and topped up with distilled water, a job for a trained person. While charging, it releases hydrogen, a flammable gas, so a well-ventilated room is essential.
• AGM: a sealed battery with the electrolyte absorbed in a glass-fiber mat. No water to add and little gas in normal use, though ventilation is still recommended.
• Gel: also sealed, with a gelled electrolyte. It is sensitive to charging settings.

All lead-acid batteries are heavy, dislike deep discharges and need regular full recharges: left half-charged for long periods, they deteriorate (sulfation).

Rated capacity vs usable capacity

Rated (nominal) capacity is the energy the battery can store, in kWh. It is sometimes given in amp-hours (Ah) and volts (V): kWh = Ah × V ÷ 1,000. For example, a 12 V, 100 Ah battery stores 1.2 kWh rated.

Usable capacity is the share you can draw without shortening the battery's life too much. It depends on depth of discharge (DoD), the percentage of capacity used in each cycle.

• For lithium LiFePO4, manufacturers often allow a large share of the rated capacity, frequently around 80 to 90%, sometimes more.
• For lead-acid, it is often recommended not to go below about half charge, to protect the battery.

As a result, for the same usable energy, a lead-acid bank needs a much larger rated capacity.

Cycles and lifespan

A cycle is one charge followed by one discharge. A battery's lifespan depends on depth of discharge, temperature, charging quality and time: a battery ages even if it is rarely used.

Manufacturers' data sheets often state several thousand cycles for LiFePO4 and far fewer for lead-acid, often from a few hundred to around a thousand depending on depth of discharge. These are laboratory figures: in real life, lifespan varies with the manufacturer and the way the battery is used. No lifespan can be promised; manufacturer and installation warranties are set out in the quote.

Heat, ventilation and salt air

Las Terrenas combines heat, humidity and salty air near the sea. Heat speeds up the aging of every battery, lead-acid in particular.

• Install batteries in the shade, in a ventilated, dry place protected from rain and salt.
• Never in direct sun or in a closed room under a roof that heats up.
• Stay within the temperature ranges given by the manufacturer.
• For flooded lead-acid: ventilation is mandatory, and no flames or sparks nearby.

See also our guide to solar panels, hurricanes and salt air.

Safety: always use a professional

A battery stores a lot of energy. A short circuit can cause very high currents, overheating and fire. Installation must be done by a qualified professional, with:

• correctly sized cables and properly tightened connections;
• DC protection (fuses or breakers) and an isolator switch;
• communication between the BMS and the inverter, where the equipment supports it;
• proper grounding and labeling.

Do not mix old and new batteries, or different types or capacities. Never open or modify a battery, and keep it out of children's reach. If a battery shows warning signs (unusual heat, smell, swelling), do not handle it, keep people away and call a technician; in case of smoke or fire, call emergency services. To have an existing system checked, we offer diagnostics and maintenance.

Sizing your batteries, step by step

1. List the appliances you want to keep running and their power in watts (W), shown on the label.
2. Estimate the hours of use for each one during an outage or overnight.
3. Multiply power by hours to get energy in watt-hours (Wh), then add them up.
4. Add a margin for inverter losses and battery aging.
5. Divide by the usable share to get the rated capacity.

Purely illustrative example: suppose LED lights, the router, the fridge and two fans together draw about 300 W on average for 8 hours. That is 2.4 kWh. With a 20% margin, you need about 2.9 kWh of usable energy. If the manufacturer allows 90% use, that means about 3.2 kWh rated in lithium; limiting lead-acid to 50%, about 5.8 kWh rated.

Two more points: the inverter must handle the power of everything switched on at once, plus start-up surges (fridge, pump). And you need to plan how the batteries will recharge: from the grid when power returns, from solar panels or from a generator. When outages come back to back, recharging matters as much as capacity. Our guide to power outages in Las Terrenas explains why.

Comparison table

Criterion	Lithium LiFePO4	AGM lead-acid	Gel lead-acid	Flooded lead-acid
Usable capacity	Large share of rated	Limited, often about half	Limited	Limited
Cycles (per manufacturer)	The most	Fewer	Fewer	Varies with care
Heat sensitivity	Sensitive; the BMS protects	Very sensitive	Sensitive	Sensitive
Ventilation	Ventilated space	Recommended	Recommended	Essential (hydrogen)
Maintenance	Very low (monitoring)	Low	Low	Regular (distilled water)
Weight for the same energy	Lowest	High	High	High
Upfront investment	Higher	Lower	Lower to mid-range	Usually the lowest

What to check during the site visit

• The appliances and hours to cover.
• The condition of any existing inverter or batteries: type, age, capacity.
• The installation location: temperature, ventilation, space, floor strength.
• Compatibility between batteries and inverter.
• Whether more batteries can be added later.
• What will happen to old batteries: lead-acid batteries should be recycled.
• Manufacturer and installation warranties, set out in the quote.

For a first indicative estimate, use our solar calculator or see the Backup package. You can also send your quote request and we will message you on WhatsApp.