Solar batteries for backup power, explained plainly
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Quick answer
A solar battery stores the power your panels make so you can use it at night or during an outage. A common do-it-yourself building block is a 12 volt LiFePO4 (lithium iron phosphate) battery. A 12.8 V, 100 Ah battery like LiTime's holds 1,280 Wh. Capacity in watt-hours is volts times amp-hours. LiTime rates its 100 Ah battery at 4,000 cycles at 100% depth of discharge. It stops charging below 32 degrees F, so keep it somewhere that stays above freezing.
Why pair batteries with solar
The U.S. Department of Energy notes that solar only produces when the sun shines, so storage lets you use that energy later. It says solar and storage can provide backup power during an electrical disruption. It also says lithium-ion is the most common battery chemistry, with lead-acid, sodium and nickel-based batteries as other options. For a prepared household, that means a battery bank that panels refill each day, so lights, a fridge or a radio keep running long after a generator's fuel would be gone.
Amp-hours vs watt-hours
Battery labels mix two units. Amp-hours (Ah) measure charge at the battery's voltage. Watt-hours (Wh) measure energy, and they are what you compare to your devices' watts. Multiply volts by amp-hours to convert:
| Battery | Math | Energy |
|---|---|---|
| 12.8 V, 100 Ah LiFePO4 | 12.8 x 100 | 1,280 Wh |
| Four in series and four in parallel (4P4S) | 51.2 V x 400 Ah | 20,480 Wh |
LiTime says its 12 V 100 Ah battery can be connected up to 4P4S, building a 51.2 V, 400 Ah system with 20.48 kWh of energy. To estimate run time, divide watt-hours by a device's watts, and treat the answer as a ceiling, not a promise.
Why LiFePO4 for home backup
LiTime lists these specs for its 12 V 100 Ah LiFePO4 battery:
- Cycle life: 4,000 cycles at 100% depth of discharge, 6,000 at 80% and 15,000 at 60%.
- Weight: 24.25 pounds. LiTime says that is one fifth the weight of 12 V 200 Ah lead-acid batteries with the same energy.
- Warranty: 5 years.
- Certifications: IEC 62619, FCC, CE, RoHS and UN38.3.
LiTime also notes this battery is meant for energy storage, not engine starting. These are maker figures, so compare datasheets model by model.
Charging rules, especially in cold weather
LiFePO4 batteries charge with a constant-current, constant-voltage (CC/CV) charger at a set voltage. LiTime lists a charge voltage of 14.4 V, plus or minus 0.2 V, and a recommended charge current of 20 A. Its temperature limits matter for preppers:
| Allowed range (LiTime 12 V 100 Ah) | |
|---|---|
| Charging | 32 to 122 degrees F (0 to 50 C) |
| Discharging | -4 to 140 degrees F (-20 to 60 C) |
| Storage | 14 to 122 degrees F (-10 to 50 C) |
So a bank in an unheated shed can still run your loads on a frosty morning, but it will not take a charge until it warms above freezing. Keep batteries indoors in cold climates, or check whether a model offers self-heating before you buy.
What you need besides batteries
A battery bank is one part of a system. You also need:
- Solar panels sized to refill the bank.
- A charge controller that matches the battery chemistry.
- An inverter to make household AC power.
- Correctly sized fuses and cables.
If that sounds like a project, an all-in-one portable power station puts the battery, inverter and solar input in one box. See our portable power station guide. For a permanent home system tied to your panel, use a licensed electrician.
What to look for when you buy
12 V 100 Ah LiFePO4 battery (example: LiTime 12V 100Ah)
Best for: Building a DIY solar backup bank one battery at a time
LiTime lists 1,280 Wh, a 100 A BMS, 4,000 cycles at 100% depth of discharge, 24.25 pounds, expansion to 4P4S and a 5 year warranty.
Watch out: It stops charging below 32 degrees F and is not for engine starting.
See options on Amazon (opens Amazon in a new tab)LiFePO4 battery charger, 14.4 V class
Best for: Topping up the bank from grid or generator power
LiTime calls for CC/CV charging at 14.4 V plus or minus 0.2 V, with a recommended 20 A charge current.
Watch out: Use a charger set for LiFePO4, not a lead-acid profile.
See options on Amazon (opens Amazon in a new tab)All-in-one power station as an alternative
Best for: People who want stored solar power without wiring a system
Power stations combine a LiFePO4 battery, inverter and solar input in one unit you plug panels into.
Watch out: Capacity is fixed unless the maker sells expansion batteries.
See options on Amazon (opens Amazon in a new tab)Questions people ask
- What is an amp hour?
- A measure of battery charge at the battery's voltage. Multiply by volts to get watt-hours: 12.8 V times 100 Ah is 1,280 Wh.
- How long do LiFePO4 solar batteries last?
- LiTime rates its 12 V 100 Ah battery at 4,000 cycles at 100% depth of discharge and 6,000 cycles at 80%. Real life depends on use and temperature.
- Can lithium solar batteries charge in freezing weather?
- Not this one. LiTime lists charging from 32 to 122 degrees F. Below freezing it can discharge but not charge.
- What is a deep cycle battery?
- A battery built to be drained and recharged many times, like a solar storage battery, as opposed to a starting battery. LiTime says its 100 Ah LiFePO4 is for energy storage, not start-up.
Sources
- LiTime 12V 100Ah LiFePO4 Lithium Battery (specifications), LiTime
- Solar Integration: Solar Energy and Storage Basics, U.S. Department of Energy