Lithium Iron Phosphate batteries – Pros and Cons

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Introduction:

Offgrid Tech has been selling Lithium batteries since 2016. LFP (Lithium Ferrophosphate or Lithium Iron Phosphate) is currently our favorite battery for several reasons. They are many times lighter than lead acid batteries and last much longer with an expected life of over 3000 cycles (8+ years). Initial cost has dropped to the point that most of our LFP battery banks break even with lead acid cost after only 4 years. In some cases, total landed cost of LFP batteries has been less than AGM due to high weight-based shipping costs. However, they must be shipped as class 9 Dangerous Goods, which can increase shipping prices in some circumstances.

 We recommend BattleBorn as a high quality LFP 12v battery at a low cost and a life expectancy of 8 to 12 years. We do not have any other 12v brands we can recommend at this time.

Pros:

  1. Extended cycle life:
    • These LFP batteries have an expected cycle life of 3000 – 10,000 cycles. This is 8 to 20 years of daily deep cycling.
    • Lead Acid batteries typically have a typical life of about 1500 cycles (4 years) in our tropical installations. Maximum lead acid life can be up to 3500 cycles, but this assumes the battery is only cycled to 35% Depth of Discharge (DOD) and always kept at 75ºF.
  2. Higher efficiency:
    • LFP batteries are 98% efficient. This means that when you put 100 amp hours into an LFP battery, you get about 98 Ah back out
    • Lead acid batteries (flooded, GEL, AGM) are only about 80% efficient. This means that when you put 100 amp hours into lead acid batteries, you get about 80Ah back out.
  3. Shorter absorb time:
    • These LFP batteries only need to reach the absorb voltage for a few minutes before they are fully charged.
    • Lead Acid batteries need between 4 and 12 hours of absorb time. This can be difficult to achieve on solar electric systems.
  4. Not damaged by Partial State of Charge (PSOC):
    • LFP batteries do not need to reach 100% State of Charge (SOC) on a regular basis.
    • Lead acid batteries need to be regularly charged up to 100% SOC. If not, they degrade. This may lead to starting up a generator during rainy season, and with the 4 hour Absorb time, this can result in using a large amount of fuel.
  5. Long shipping times, furloughs, and extended absences:
    • These LFP batteries will not, under normal circumstances, suffer from long shipping times. These batteries can also be stored unused for up to 1 year with no maintenance.
    • Lead acid batteries will degrade after only 3 months in shipping. Furloughs and extended absences can also damage lead acid batteries.
  6. High temperature operation:
    • These LFP batteries can be operated at any temperature between 32ºF and 120ºF, with little degradation.
    • Lead acid battery cycle life will degrade quicker at higher temperatures. For every 15ºF above 75ºF the cycle life of a lead acid battery is reduced by half.
  7.  Lightweight:
    • At only 30lbs each, a typical LFP battery bank (5) will weigh 150lbs.
    • A typical lead acid battery can weigh 180 lbs. each, and a battery bank can weigh over 650lbs.
  8. These LFP batteries are based on the Lithium Iron Phosphate chemistry, which is one of the safest Lithium battery chemistries, and is not prone to thermal runaway.
  9. We offer LFP batteries in 12 V, 24 V, and 48 V

Cons:

  1. Price: An LFP battery will cost about twice as much as a equivalent high quality AGM battery.
    • Typical return on investment is 5 years, when an AGM bank would need to be replaced.
    • If you will only need batteries for 4 to 6 years, lead acid may be a better choice
  2. Low reserve capacity:
    • Because of price and intended cycle depth, LFP batteries will have a very small reserve capacity (about 20%) designed into the bank. Offgrid Tech has a design target of 65% Depth of Discharge (DOD) daily, (discharging down to 35% State of Charge [SOC] daily). This leaves very little power left over in reserve. We do not recommend discharging these LFP batteries lower than 85% DOD (15% SOC). This may mean a user may need to run a generator or reduce loads more often.
    • Lead Acid battery banks are designed with reserve capacity in mind (about 45%). A typical lead acid battery bank for a solar electric system will be designed to be discharged to 35% DOD (or 65% full SOC) on a daily basis. This leaves 65% in the batteries as a buffer. Lead Acid batteries can, on occasion be discharged all the way to 80% DOD (20% SOC).
  3. Subject to damage if over or under charged
    • High voltage (15 volts or higher) can damage an LFP battery.
    • Over discharging an LFP battery to the point where it turns off is also potentially damaging.
    • It is very important than an LFP battery never be over charged (Use high quality equipment) and just as equally important to never let the batteries get completely empty (monitor the voltage and charge via generator when low).  We do not recommend leaving BattleBorn batteries connected to loads but unattended for more than 2 weeks.
  4. May be more susceptible to lightning damage.
    • LFP batteries have sensitive electronics inside each battery. These can potentially be destroyed by voltage spikes and surges from nearby lightning strikes. Surge suppression is built into the battery combiner box to help mitigate this possibility.
    • Lead Acid batteries have a much smaller chance of being damaged by a nearby lightning strike, unless the charging equipment is damaged and the batteries don’t receive adequate charge.
  5. Shipping: The small and light form factor of these batteries can make them easier to transport. However, these are a lithium battery technology and are fully regulated as dangerous goods under UN3480 regulations. All shippers must be certified to UN3480 certification before they are legally allowed to ship these batteries. In some circumstances this can lead to high fees and even refusal to transport.