The State of Charge Gauge is a string of LEDs which display the following:

1. When the lights are static the LEDs act as a battery discharge indicator (BDI).
2. If there is a single light flashing it is displaying a Device Trouble Code (DTC).
3. If the lights are turning on in series it is confirming the pack is charging.

Flux Power’s patented Battery Management System (BMS) monitors charging so that the pack cannot be over charged or over discharged.  The only risk is if someone fully discharges the battery pack and then does not plug it in.  In this case, because of the small parasitic draw from the electronics, it is possible to completely kill the pack.  Therefore, we recommend the packs remain plugged in whenever not in use for more than a few days.  There is no harm in leaving the packs plugged in, but great harm if they are left discharged for extended periods of time. 

Note:  Allowing the battery to over discharge due to extended use or storage after the low SOC alarm goes off will results in an “over discharge” condition and the battery will no longer charge.  Failure to properly maintain the batter will void the batteries warranty

There is no point at which a discharge counts as 1 cycle.  Each cycle puts wear on the battery proportional to its depth of discharge.  If the battery is discharged to 80% every cycle, it will last ~ 2000 cycles.  If the battery is cycled at 70% DOD, the battery will last ~3,000 cycles. 

This has a nonlinear effect on the total amp-hour throughput of the battery over its lifetime.  The smaller the DOD is, the larger the total Ah output of the battery is.  Comparing the lifetime output of two 100 Ah batteries at 80% and 70% DOD, the total Ah output can be idealized by the following:

100Ah*0.8DOD*2000=160,000Ah total output.

100Ah*0.7DOD*3000=210,000Ah total output.

In reality, the total lifetime output numbers will be closer together, as factors such as battery aging are not being considered, however the 70% DOD battery will still output more Ah over its lifetime.  This is the main reason why opportunity charging is a perfect fit for LiFT Packs.

There are several different chemistries available.  Flux Power uses LiFePO4 due to its long cycle life, low cost of ownership, thermal stability, and high-power output.  Below is a chart which provides some information on alternative lithium-ion chemistries.

As lithium iron phosphate cells cycle, the charge is carried between the anode and cathode using lithium-ions.  As the pack cycles a very small percentage of the mobile lithium-ions are caught in irreversible side reactions.  This reduces the amount of charge transfer possible between the electrodes. 

In lead acid this is somewhat analogous to sulfation, where the sulfur becomes locked in stable lead sulfite crystals and can no longer intercalate into the lead plates.  Sulfation is worse however as it occurs during use and during storage, the crystals can grow and crack the plates, and block electrolyte access to the plates.

When the battery charges, the lithium ions are in the carbon/graphite anode, and when discharging the lithium ions move to the cathode. The chemical reactions are as follows:

• Charge : LixC6 = 6C + xLi + xe
• Discharge : Li(1-x)FePO4 + xLi+ xe = LiFePO4

It is difficult to compare a lithium-ion and lead acid battery when only looking at amp hours.  Flux Power uses amp hour equivalent to give a better estimate of the run-times you should expect.  The voltage is higher and stays higher, meaning there's more energy (kWh) in the battery pack, for a given amp hour rating. 

In addition the pack is lighter, and the chemistry is more efficient, so you save energy charging and discharging, and use less while running the equipment.  You can also drain more of the energy from the battery without serious effects, meaning for identical amp-hour ratings, lithium-ion will run longer.  This is why we call our 100Ah lithium-ion pack a 135.  It will run as long (or longer) than a 135Ah lead acid.

Recycling methods are currently being developed, with reports of 60% recyclability at the cell level.  Lithium-ion batteries are the future of energy storage, and recycling efficiencies are predicted to climb to >90% as the markets scale and additional recycling methods are developed.  Until a mature recycling program is available, Flux Power agrees to take back any battery at the end of its usable life for either recycling or repurposing. 

Also note, because lithium-ion batteries have a much longer life-time vs. lead acid, there will be dramatically fewer batteries subject to recycling over time.  If you require more detailed information regarding recycling, please contact your Flux Power representative.

There are several factors responsible for the remarkable safety of Flux Power lithium-ion batteries.

1. The selection of battery chemistry is important. There are several lithium-ion chemistries to choose from, and each has unique properties.  Flux Power has chosen lithium iron phosphate (LiFePO4) for several reasons.  Most importantly LiFePO4 is chemically stable and has the highest thermal runaway temperature of any lithium-ion chemistry at 270 °C (518F).  The news stories of cell phone and laptop batteries catching fire were a cobalt based chemistry that is less chemically stable.  These batteries are also in a small cylindrical cell format.
2. The lithium-ion cells used are in the form of large pouch and prismatic cell technology versus cylindrical cell. The pouch and prismatic cells contain >20Ah versus the 2.5Ah in cylindrical, meaning LiFT Pack batteries have up to 10 times fewer power connections.  In addition, the cells are connected with flexible busbars, meaning they are extremely vibration resistant.
3. The use of Large Format Cells means there are far fewer cell taps and temperature sensors. This system is less complex and inherently safer.
4. The BMS monitors the cell temperature and current and shuts the system down if it detects anything which may cause harm to the battery. This is to maintain battery performance and expected lifetime.

The lithium-ion cells are first encased in hard plastic, and then an industrial 10-gauge powder coated steel case.  If a user punctures through all these materials and exposes the lithium-ion cell electrodes and electrolyte, be cautious when handling.  The electrolyte consists of organic solvents (EC, PC, DEC) and a dissolved electrolytic salt (LiPF6).  They are skin and eye irritants, and fumes can cause mucus membrane irritation. 

The solvents are flammable so do not expose to an open flame.  Use rubber gloves, eye protection, ventilation and positive pressure breathing protection when removing the damaged battery and electrolyte.  In addition, LiPF6 is hydrophilic and reacts with water releasing hydrogen fluoride, a corrosive flammable gas.  If a fire does occur, use a CO2 or chemical fire extinguisher.

Flux Power uses lithium iron phosphate (LFP) in its products as it is a very stable chemistry.  The burn temperature is over 500F, much higher than other chemistries such as lithium cobalt at 149C (300F).  The chemical stability also provides long cycle lifetimes (2000 at 80% DOD). In addition, there are safety measures built into the pack which prevent overcharging and rapid discharging.  Finally, the battery case is made of high-grade steel, protecting the cells from damage, and containing them should a cell breach occur. 

All these protections mean that under normal usage there is no danger of a fire.  The dangers of spills and explosive gas buildup from lead acid batteries are much more common than a LiFT Pack catching fire.

Lead acid:

When a single cell fails, there is no BMS to manage the charging.  Therefore the failing cell will heat up, but not fully charge.  The failing cell will accelerate its decline as it is used improperly and cause the entire pack to drain rapidly when in use.  As an example, if a failing lead acid cell is at 50% capacity, the charger will not attempt to charge it to its full (diminished) capacity, this means that once the pack is used, the voltage drop will be significant in this cell, and the entire pack will see a drastic drop in run-time due to the low voltage in this cell.

Flux Power lithium-ion battery:

When a single cell begins to fail, the entire pack will experience a reduction of run-time proportional to the single failing cell’s reduction in run time.  The BMS will still charge and balance the cells, but the pack will cut off when the failing cell voltage drops to 2.8 Volts.  As an example, if the failing cell is at 50% capacity, the charger will still charge the cell to full (diminished) capacity and the cell will produce the expected voltage, just for 50% shorter run-time.  The pack will then run as if it has 50% capacity.  The BMS will protect the other cells from harm due to a low cell.  The BMS avoids the low voltage scenario which is problematic in lead acid.

Lithium-ion cells have a higher nominal voltage than lead acid.  The Flux Power LiFT pack is comprised of an array of 8 lithium-ion cells connected in series or parallel, each with a nominal voltage of 3.2V.  The pack nominal voltage is therefore the summation of the number of cells in the battery.  There is minimal voltage drop as the pack discharges under normal use.  The pack will indicate it needs to be charged when it drops to 3.0 volts per cell.  See the table below for a summary of the different lithium-ion nominal voltage compared to lead acid nominal voltage.