Technical tips

Why lithium batteries - part 2

Lithium Ion Battery

The best battery technology available for putting together an energy storage system is based on lithium ION . Are you also looking for energy savings and less fuel consumption which also reduces emissions? Would you like to make an investment in a battery set that has the longest lifespan and the best Total Cost of Ownership? Do you always want to be able to work without worrying about the energy supply? Then choose Lithium Ion batteries.

WhisperPower offers the best solution for the different user groups. The Whisper Power Lithium Ion Power Plus (LFP) series is of unparalleled top quality and is ideal for larger battery storage systems. The unique combination of state-of-the-art technology and smart software makes this Li-Ion Power Plus battery a robust, safe and easy to use battery buffer where large inverters and battery chargers can be connected. The ION Power Plus are true system batteries.
They are ideal for 24 / 48 VDC systems that need more battery capacity and where large inverters are connected for a quiet emission-free 230 V supply. For example the WhisperPower AC PowerCube Super Inverter with capacities of 7kVA and 14kVA or even more. The ION Power Plus batteries can be charged with high charging currents (1/C) so they can be quickly recharged by fast charging systems based on battery chargers and for example solar power. If the batteries are part of a total system with a generator, the generator running time will be significantly reduced and thus fuel consumption and emissions as well.
Compared to conventional lead-acid batteries, the WP-Ion Power Plus lithium batteries offer an enormous amount of energy in a compact housing. As a result, there is a large saving in weight and a space saving of up to 70% due to the compactness of these batteries. The batteries are very efficient and have extremely high performance making it the ideal battery for high power systems.
The ION Power Plus battery uses the safe lithium-iron phosphate (LiFeP04, also abbreviated as LFP) technology. With the integrated battery management system (BMS) and canbus connection, the Li-ion battery is protected against deep discharge, overcharging and overheating. This makes it the safest lithium battery type there is.

! Attention! An external circuit breaker (bi-stable relay) is always required!

Specific Characteristics

  • Very compact and lightweight, up to 70% lower than the known lead-acid batteries.
  • They have an extremely long lifespan, over 3500 cycles when charged 1C and Depth of Discharge 100% (DoD), which means they last a long time and do not require battery replacement after several years. When DoD is lower than lifetime will increase even further.
  • The total efficiency of ION Power Plus is 97% as opposed to 82% for lead-acid batteries.

Safety first

The BMS (Battery Management System) takes care of the active balancing of the cells. The disconnection protection is placed externally. Whisper Power supplies the so-called WIB (WhisperPowerInterfaceBox) developed with a bi-stable relay for switching off the DC consumers at (too) low or too high voltage. When assembling the battery system, this component must be taken into account as a complete system solution. Regularly we are told that people buy the batteries themselves where these protections are not provided. This can quickly lead to dangerous situations.

Battery Capacity

The available battery capacity is 100% this in contrast to lead-acid batteries where often only 50% of the battery capacity is available.

  • Extremely long lifespan.
  • Long Cycle life.
  • Charge the Li-ion battery when the charge level drops below 20% to extend the life of the Li-ion battery.
  • If the state of charge (SoC) drops below 20%, you need to charge the batteries . At least you should always keep the voltage of the Li-ion battery above 10V.

Operation voltage

12V – 750VDC

How do I select the right battery for my application?

  • the battery voltage and minimum and maximum system voltages.
  • the battery capacity in Ah must be matched to the rated current consumption and the running time of the consumption in combination with recharging time. This can be done by means of a load balance see also the previous tip.
  • the maximum discharge current of the system should be carefully tuned to the battery specification. Where necessary, a battery set with a larger capacity should be selected to prevent overheating.
  • the maximum allowable weight and the maximum dimensions in the room where the batteries will be installed.

! Warning! Never charge the Li-ion battery too long, this will cause the Li-ion battery to malfunction permanently. Always use a battery charger that automatically stops the charging process when the Li Ion battery is full.

Charging time

The Li ION Power Plus batteries can be charged with 1C. This means that in just over an hour they will be charged from empty (0% SoC = Stat of Charge) to full (100% SoC). 1C indicates once the capacity of the Li-ion battery, i.e. a 160Ah battery that can be charged with 1C with 160A. Suppose we charge with C3 then we charge with about 55 Amps and the battery will be charged in about 3 hours. During charging always use the indicated charging current and end of charging voltage. For the most optimal lifespan 3C is recommended but in some cases we go to 1C which will result in shorter generator run time.

Charging method for Li Ion Power Plus

We recommend applying the following charging method “Constant Current Constant Voltage” (CCCV) charging method. The CV part of the charging is also used to balance the cells of the Li-ion battery and thus extend the life of the Li-ion battery.

Charging phases

  • Bulk phase.
  • Absorption phase.
  • Float phase.
  • Maintenance phase, this is optional and depends if the Li-ion battery is not regularly up to 100%.

Charging phase CC of CCCV

In this phase (CC part of CCCV) the Li-ion batteries are charged with a constant current.
until the end of the charging voltage (Uabsorption). When Uabsorption is reached, the charger switches to the absorption phase.
On some chargers the time t0 can be programmed. This is a safety measure which stops the charger if the bulk phase takes too long. Time t0 depends on the charging current and the Li-ion battery capacity. If this option is available, t0 can be calculated and set


  • t0 : the bulk time in hours.
  • Cbat : the rated battery capacity in Ah.
  • Ich : charger charging current in Amps.

The factor of 1.2 is due to the fact that the Li-ion battery has more capacity than its nominal value and the current measurement inaccuracy of the charger.
If there is also power consumption during charging, this should be taken into account because the charging current will be less.
Below is an example of empty Li-ion batteries that are charged with a 12A charger. The
Bulk phase takes longer at higher nominal capacity. Suppose 160 Ah and the charging current is 40 Amps then the t0 = 4.8 hours.
To shorten the bulk phase the battery charger capacity can be increased.

In this phase (CV part of CCCV) the charging voltage is kept constant at Uabsorption to fully charge the Li-ion battery and balance the battery cells.
The charger must provide a current low enough to balance the cells. The balance current is max. 2A for the Li Ion Power Plus.
The duration of the absorption phase can vary, as it strongly depends on the age and condition of the Li-ion battery. When the absorption time t1 is over, the charger switches to the float phase.

Float phase

In this phase, the Li-ion battery is no longer charged. The output voltage of the charger is set to Ufloat Voltage. If there are devices that draw power from the Li-ion battery, the charger will support the battery or power all devices. All chargers of Whisper Power have a float phase, of course depending on the setting of the battery charger. Usually the float phase will have a minimum voltage of 13.6V and a maximum voltage of 13.9V and will typically be 13.8V. For 12 and 48 Volt these values have to be multiplied by 2 or 4.

Discharge during the float phase

During the float phase, the charger delivers the load. However, if this load is higher than the charging current, the battery will also have to deliver part of the load. In this case, if the battery voltage drops below Ureturn (usually 12.8 Volt), the charging process is repeated. A new bulk phase (t0) followed by an absorption phase (t1) starts again.


When stored, the Li-ion battery must be disconnected from all loads (including CAN) and chargers. In this condition, the self-discharge of the battery is less than 3% per month.
! Warning! Please follow the storage guidelines for each Whisper Power Li-ion battery that are available
in the respective owner’s guide.

Maintenance during storage

The battery should be recharged every 3 months.

End of storage

At the end of a storage period and before the Li-ion battery is used again, the battery fully charged.
! Warning! When used in systems, all Li-ion batteries must be fully charged before installation . BE SURE you have all batteries with 100% SoC (charging status) before combining batteries to form a battery set.