(Last modified on January 26th, 2022.)
So you’re considering investing in a battery backup system. The first thing you need to decide is how you want to use them. Will your batteries kick in for emergencies only, or will you use them daily to off-set peak usage charges? Do you want to back up your entire home/business or only critical loads (like the fridge, your stove, a few lights, etc.)?
These will be the main factors in deciding what size battery you choose. But what should you look for in a good battery? Besides price, we recommend looking at chemical composition (lead acid and lithium iron phosphate are the most stable, non-combustible compositions), longevity, efficiency and depth of discharge. All of these factors contribute to a long lasting and reliable battery backup system.
Below is a break down of batteries we recommend, categorized by chemical composition and manufacturer. We’ve also addressed all of the considerations mentioned above for an easier comparison of products. Sun Pacific Solar can buy and install any type of battery, but we are particular about the products we adopt because quality and reliability are very important to us.
Depth Of Discharge (DOD)– refers to the percentage a battery can discharge. However, this is usually different from the DOD percentage manufacturers specify not to exceeded so as to not wear out the system. Exceeding the latter can void warranties.
Lifecycle/longevity– the number of times a battery can be cycled at a certain DOD. This can be translated into years to calculate an approximate longevity.
Efficiency– some energy is lost in the charging process, so the efficiency percentage refers to the remaining amount of energy available for use.
Flooded– contains liquid electrolytes and requires adding distilled water.
Dry/Sealed– same chemistry but sealed and non spill-able.
Lithium Iron Phosphate (or LFP/Lithium Ferrous Phosphate) Battery Storage
Lithium Iron Phosphate battery storage requires zero maintenance, can be installed anywhere in your home because they don’t off-gas and are more efficient than lead acid batteries (round trip efficiency is 98% vs 85% for lead acid). LFP batteries also don’t require a full recharge on a daily basis, unlike lead acid batteries. The major drawback of Lithium Iron Phosphate batteries is that they are expensive, but they have a much longer life cycle than lead acid batteries.
Sonnen batteries have a long lifespan (rated for 10,000 cycles or over 27 years) and have very advanced programming (allowing for time of use shifting/energy arbitrage, backup & self consumption). They have a 95%-100% Depth of Discharge range and 86%-98% efficiency rating. Sonnen batteries use an OutBack inverter as part of their technology. The drawbacks to a Sonnen battery storage solution is it’s limited size (20kWh maximum), meaning the systems are not scaleable.
Because we are a Sonnen dealer, our customers receive an extended warranty. Sonnen batteries are warrantied for 12 years and 3 months from the date of purchase, 12 years from the date of installation, or 12,000 full (100%) charging cycles of the battery pack, whichever comes first. The warranty covers all defects in materials and workmanship, and will repair or replace the defective part free of charge. However, Sonnen will not cover labor or shipping costs.
SimpliPhi is a local company (based in Oxnard, California) and has been operating since 2002. Their battery backup solutions are scaleable from 3.5kWh up to several hundred and have a long lifespan of 10,000+ cycles at 80% discharge. SimpliPhi batteries are 98% efficient and have a depth of discharge up to 100%.
Depending on the model, SimpliPhi Core Power units have either a 5 year or 10 year limited warranty or 10,000 cycles, whichever comes first. Fully-Integrated Systems have a 2 year limited warranty on defects in workmanship and materials. It does not cover damages caused by or resulting from shipping or transportation, or a product that did not undergo scheduled maintenance measures in compliance with instructions. The warranty does not cover the cost of installation, removal, shipping or re-installation.
Blue Planet batteries have great monitoring software, have a long lifespan (8,000 cycles at 100% DOD, or over 21 years), are scaleable up to 450kWh and have very fast charging/discharging (up to 90% in 1 hour). Blue Planet batteries have 98% efficiency and a Depth of Discharge of 99% at full power.
Blue Planet also has the longest warranty of its competitors. They offer a 10 year product warranty/15 year performance warranty.
Lead Acid Battery Backup
The main incentives for lead acid battery backup is that these batteries are generally more cost effective than LFP’s and are manufactured from recycled materials, making them up to 99% recyclable. Lead acid batteries come in two chemical compositions, either flooded or sealed. Flooded batteries are generally less expensive than sealed (Rolls, OutBack, Trojan are all at a similar price point).
Lead acid batteries will typically last 3 – 6 years if they’re cycled daily (15 – 20 if they’re only used for backup and depending on frequency of grid outages) however, they must be recharged to 100% daily or their lifespan will decrease. They also require ventilation because of their off-gassing and can’t be installed in your home. This means you need to have space in your garage, shed or other non-living quarters to install them. Additionally, lead acid batteries require yearly maintenance.
OutBack produces both flooded and sealed lead acid batteries, as well as nano carbon models. These models differ in price, longevity, and warranty but are all viable options for battery backup solutions.
OutBack sealed lead acid batteries require less maintenance than flooded batteries and have a longevity of 1800 – 3000 cycles (depending on the model) at 50% DOD. OutBack sealed lead acid batteries have a maximum DOD of 80% and some models have up to 95% efficiency. However, sealed batteries are more expensive than flooded models, have a limited warranty and have minimal off-gassing requiring ventilation.
OutBack sealed lead acid (AGM) batteries have a 2 – 6 year warranty, with or without full replacement depending on the model. This warranty covers repair or replacement for defects in workmanship and materials. The warranty does not cover damage caused by shipping, transportation, installation or removal, or damage caused by routine or daily discharge of more than 50% capacity. It also does not cover costs of installation, removal, shipping or reinstallation. The warranty is transferrable.
OutBack flooded lead acid batteries have a depth of discharge of 80% and have a longevity of 1200 – 2800 cycles at 50% DOD (depending on the model). Flooded batteries are also more cost effective than sealed. However, they require adding distilled water on a regular basis and they have high levels of off-gassing so they must be installed in a garage, shed, of other non-living quarters with adequate ventilation.
OutBack lead acid flooded batteries have a 2 – 4 year full replacement limited warranty (depending on the model) that covers repair or replacement for defects in workmanship and materials. The warranty does not cover damage caused by shipping, transportation, installation or removal, or damage caused by routine or daily discharge of more than 50% capacity. It also does not cover costs of installation, removal, shipping or reinstallation.
The OutBack nano carbon batteries have a depth of discharge of 80% and a lifecycle of 2600 cycles at 50% DOD. They also have the advantage of not needing to be recharged to 100% each day. Nano carbon batteries have a 2 year full replacement warranty that covers repair or replacement of defective products. However, it does not cover labor or shipping costs, nor does it cover routine or daily discharge of more than 50%.
Rolls Battery Engineering
Rolls’ flooded lead batteries have the longest life cycle of any flooded battery and they are the highest quality lead acid batteries. However, they have a slightly higher price point than other flooded batteries. Rolls batteries have a depth of discharge of 80% and a lifecycle of 950 – 3750 cycles at 50% DOD (depending on the model).
Rolls Battery has a 1 – 10 year warranty on their batteries, depending on the model. Within these warranties, Rolls offers a 1 – 3 year full replacement or repair period, as well as a 1 – 7 year pro-rated warranty period. These warranties cover defects in workmanship and material, but do not cover shipping, transportation or installation/removal costs. The warranties also do not cover shipping damage, batteries that have been subject to discharging beyond the recommended depth of discharge, improper maintenance, repair, removal, installation or storage.
Trojan’s flooded lead acid batteries are the most cost effective flooded battery out of the above competitors. However, they require ventilation because of their have high levels of off-gassing and require the addition of distilled water on a regular basis. Trojan batteries have a lifecycle of 600-3600 cycles at 50% DOD (depending on the model), and have a depth of discharge of 80%.
Trojan offers a 1 – 10 year warranty on their batteries, depending on the model. Within theses warranties, Trojan offers a 3 – 12 month free replacement or repair period, as well as a 4 – 120 month pro-rated credit period, the duration of which depends on the battery model. These warranties cover material and workmanship defects, however they do not cover expenses for transportation or installation, damage from shipping, improper maintenance, or depth of discharge beyond that recommended by the manufacturer.