Lithium-ion Battery Safety

When using your rechargeable Radenite battery, it's important to understand the environmental and operating parameters within which the battery must be maintained to ensure safety and good performance.

The power density of Lithium-ion batteries has revolutionised portable power applications, energy capture/storage and transportation. When used incorrectly however, rechargeable Li-ion cells and batteries are less "forgiving" than the NiMH, Ni-Cad and Lead Acid alternatives. Cells have a very narrow tolerance level for their charge and discharge currents. The cells must also be kept within a defined voltage range. Radenite's batteries provide some protection against voltage and current anomalies, but much depends on how the battery is deployed to ensure safe use, extended life and optimum performance.

The following sections provide additional essential information on the safe use of your Li-ion and LiFePO₄ batteries.

If you are unsure about the safe use of your Radenite battery, disconnect it from any charger and/or load equipment and contact Radenite immediately.

What to do if your li-ion battery overheats or catches fire

If a Li-ion battery overheats, hisses or bulges, then it's possible that one or more cells are in "thermal runaway". If it's safe to do so, immediately move the battery away from any flammable materials and place it on a non-combustible surface. (Use oven gloves or tongs if available). If possible, place the battery outdoors to burn out. If a fire is uncontrollable, contact fire emergency services. Disconnecting the battery from a charger may not stop thermal runaway.

A small Li-ion fire can be handled like any other combustible fire. Ideally, use a foam extinguisher, CO2, dry chemical, powdered graphite, copper powder or sodium carbonate to extinguish any fire. If no foam or powder based extinguisher is available, use water to extinguish a fire. (There is very little lithium metal in a lithium ion battery to cause a significant adverse reaction). Water also cools the adjacent area and prevents the fire from spreading. Covering the battery with a fire blanket may help contain the combustion.

How do I charge my battery?

Adhering to the recommended Charge and Discharge (Load) currents is essential to avoid battery failure and fire risk.

Note: Never leave a Li-ion battery charging unattended.

Check the specifications of your battery and ensure that you do not exceed the load limits during discharge (usage).

The same applies to charging rates. Radenite batteries are marketed with matched chargers that will deliver current within safe limits and the correct final voltage to your battery. For example, the Radenite 1500mAh 12V LiFePO₄ battery should not be charged with a current higher than 1500mA. Common domestic "wall-wart" chargers will often be rated at 2A (2000mA). These should not be used. Moreover the voltage of a fully charged 12V LiFePO₄ battery is 14.4V (3.6V x 4). A standard "12V charger" typically delivers 12.8V. This may result in a battery charged to only 50% of its capacity.

Do not attempt to charge the battery with a voltage higher than the battery's specification.

36V Li-ion batteries require a 42V supply to reach full capacity. A 36V charger will take your 36V battery to only ~50% of its useful capacity.

• Never use a battery charger that exceeds the charge current specification of your battery
• Never connect your battery to equipment that draws more current than the battery's discharge current specification

Unless marked with a prominent IP65 label your Radenite battery is not waterproof and should not be exposed to liquids or damp environments. Ensure that the battery is deployed where the ambient temperature does not exceed 60°C.

Prolonging the life of your Radenite Li-ion battery

Aside from following the preceding essential safety advice and the required parameters related to charge and discharge currents, there are two significant contributions you can make to extending the operating life of your battery.

1. Depth of discharge. Specifications assume a full discharge (100% Depth-of-Discharge or DoD) of a battery before recharging is performed. This then yields a the number of re-charge operations that the battery can absorb before the performance degrades. In broad terms, after ~800 re-charge operations, Radenite Li-ion batteries will be able to deliver ~70% of their initial capacity. If you have control of when the re-charge cycle is performed, you can significantly increase residual capacity, extending the life of your battery, by performing a recharge before the capacity is exhausted; ideally before the DoD reaches 40-35%, but the performance should remain within warranty limits to an 80% DoD.

   
   LiFePO₄ batteries can endure regular 100% DoD before recharging. This gives them a singular advantage over Start Light Ignition (SLI) batteries. Radenite LiFePO₄ batteries are NOT a substitute for SLI batteries; they are incapable of delivering the cold cranking amps to start a car engine. Using them for these purposes may damage cells, the battery or the BMS and void your warranty.

   
   

2. Charge cut-off voltage. The maximum specified charging voltage for Li-ion is based on the manufacturer's highest estimation of a safe State-Of-Charge to ensure maximum Watt-hours capacity. However, if you have control of the cut-off voltage, you can again extend the life of your battery substantially by charging it just shy of the maximum charge voltage. For example, instead of charging a 36V battery to its full 42V, a 41V charge cut-off will reduce the formation of a coating on the anode which will, over time, reduce the life of the battery by increasing its internal resistance. The accretion rate of this "Solid Electrolyte Interphase" increases with final charge voltage. The trade-off is slightly-reduced capacity. (Approximately 93% in the 41V example).

I want to put my batteries into storage

Ensure the batteries are in a 50% charged state (An approximation may be used from the battery voltage: 3.2V per series cell for LiFePO4 and 3.6V per series cell for Li-ion). Then cover the terminal connections in electrical insulating tape and store in a dry environment between 10°C and 25°C. Check each month if the battery is approaching lower voltage threshold (all cells discharge naturally over time) and charge if necessary to 50%.

I need help choosing a battery

If you are replacing a lithium battery, then the specifications of the existing battery will help guide you to the right type of battery (eg Li-ion vs LiFePO₄) and whether it will fit in the space you have allocated (form factor).

Battery Electrical Characteristics

But whether you are replacing or purchasing for the first time, ensure that you know the correct voltage of the battery you require, the maximum current that the battery will be expected to deliver and the capability of any new (or pre-existing) charger to ensure that battery charge currents are not exceeded.

Battery Charge and Discharge Currents

Special consideration must be given to the current with which you will charge your battery and the current which you expect your battery to delivery. Again, unlike their lead-acid counterparts, lithium batteries are less tolerant of excessive currents. Make sure you understand the specification of the battery you are buying and verify that it will deliver the continuous current you are seeking.

In particular, although LiFePO₄ batteries will meet the voltage requirements for most lead-acid replacements (6V, 12V, 24V etc.), lead-acid batteries have an extremely low internal resistance and can deliver very high currents in comparison to most LiFePO₄ equivalents. Therefore, while the capacity (Amp Hours(Ah) or Watt Hours(Wh)) and voltage of a LiFePO₄ battery might seem a good match, it may not be able to deliver the current (or Cold Cranking Amps) required to start an engine.

Li-ion vs LiFePO₄ Comparison

Lithium-ion batteries have more than twice the energy capacity of LiFePO₄ batteries on like-for-like volume and weight comparisons. Many Li-ion batteries can deliver higher currents and can accept a higher charge current compared to LiFePO₄. There are specialist LiFePO₄ batteries that can accept and deliver higher currents (for example, those designed for starting car engines that require 100s of CCAs), but in the non-specialist category, Li-ion exceeds LiFePO₄'s capabilities.

However, LiFePO₄ batteries have several unique advantages over Li-ion:

• The cell voltage is convenient for replacing existing LA or SLA batteries.
• They are generally less expensive than Li-ion batteries
• They can generally be charged recycled more times than Li-ion or LA/SLA
• Their performance is impacted less by deep charge recycling (ie fully discharging before recharging)
• They are more forgiving if used incorrectly (i.e. outside the specified current and voltage ranges)
• They do not suffer from inherent thermal runaway characteristics (fire risk) making them a substantially safer technology