Are your rechargeable batteries maintenance heavy?

Rechargeable battery chemistries have advanced significantly in recent years.  Lithium-ion has emerged as the go-to battery chemistry for a wide range of devices, from home applications such as smartphones and cordless power tools, to industrial Medtech and military equipment.

As cell technology improves, battery maintenance demands reduce.   However, maintenance is still one of the biggest challenges faced by OEMs and their end users.   In order to maximise a battery’s performance over a longer period it is advisable to store it correctly, monitor the capacity level and use a battery management system.   Here we not only discuss each of these performance improvers but also how to discard a battery once it reaches end of life.

Storage

Recommendations for the optimum way to store rechargeable batteries varies based on the chemistries they use.   For example, lead acid ones should be fully charged before storing as partial charge causes sulfation, whereas NiCd may be stored on empty but need exercise after a lengthy period of dormancy.

Lithium-ion cells are ideally stored at between 40% and 50% state of charge (SoC) as storage at very high or low states of charge is not recommended.   Storage at a high rate can lead to a permanent loss in recoverable capacity whilst storage at a low rate can lead to copper dissolution, short circuit and failure. 40% to 50% SoC is a happy medium which provides sufficient capacity for the cell or battery to exist in the supply chain for a significant period without the need for recharging, and also promotes enhanced safety as less energy is present.

Continual battery R&D is making vast strides to reducing the maintenance requirements and extending service life, however it is still important to closely monitor a battery’s health to enable replacement at the appropriate time.

Capacity

One of the best ways to diagnose when a battery is ready for replacement is by setting a capacity level that it cannot fall below (of around 70 or 80% - varies by application).   Putting lower capacity batteries to less demanding uses can prolong this.   For example, Accutronics’ credit card sized products are ideally suitable for use in portable electronics but are not so well-suited to power draining Medtech on 10-year PDLCs, whereas the Accutronics’ CMX series would be a better fit. 

Removable or easily replaceable portable power should be selected for devices that are required to last for up to 10 years, as the device is likely to outlive the battery.  Nonetheless longevity improvements are happening:  The Department of Energy has found that ‘every year roughly one million usable lithium-ion batteries are sent in for recycling with most having a capacity of up to 80%’ (Battery University), which has a negative impact on the environment.   A growing trend with electric vehicles, which may extend to other Li-ion applications in the future, is second use as ‘retired EV batteries usually [hold] residual 70 ~ 80% energy capacities’ (IEEE Xplore) so can be further utilised as ‘stationary energy storage devices’ (Mercedes Benz), a cost-effective option.

Battery Management System

Any cost saving, that is not at the expense of quality or performance, must be positive.   Devices such as commercial livestock feeder systems, robotics, floor cleaning machines and automated ticket machines have traditionally used sealed lead acid (SLA) chemistry which is costly to maintain.

Therefore OEMs should consider replacing them with lithium iron phosphate (LFP) such as Ultralife’s range of lead acid replacement solutions, which can deliver as much as twice the energy of SLA.   LFP technology can be used with a battery management system (BMS) to optimise the runtime, balancing and protection system.   Ultralife’s BMS outperforms off-the-shelf alternatives by considering how the battery performs in a range of temperatures and environmental conditions.

No longer maintainable?  Dispose!

Manufacturers in the U.S. are not currently collecting Lithium batteries for recycling, so they should be correctly disposed of after use.  No federal regulations are applicable to the disposal of lithium but individual states or localities can establish their own guidelines and should be contacted.  Full guidelines on the recommended disposal of Ultralife products can be found on the FAQ section of our website.

For more advice on the effective maintenance of Ultralife rechargeable products, please