Medical implants: why consider rechargeable batteries?

But when a non-rechargeable battery reaches the end of its useful life, an invasive surgical operation on the patient is required to replace it. And long-term costs can be higher for non-rechargeables, even with a lower up-front price.

Today, rechargeables should be considered for all medical implantable devices – both for technological reasons, and because of the shift to ‘accountable care’.

Technology trends 

Rechargeables do have some drawbacks: they cost more initially, as they are more complex, and must be sold with a charger. This is balanced by longer lifetime and lower ‘through-life’ costs, with less frequent operations required for battery replacement.

The patient must sit connected to a charger every few days, and the charging circuitry restricts the depth below the skin to about six millimetres. Charging rates are improving though, with typical charging times coming down from two hours to one, or even less.

Rechargeable batteries are smaller than primary alternatives, so are favoured by today’s trend towards device miniaturisation. Another trend is that new devices may need much higher power, so the useful life of a primary battery would be short.

Overcoming patient non-compliance 

Rechargeable batteries haven’t been approved for life-sustaining applications, because patients might lose or break their charger, or simply forget to charge the battery. For other implantable devices, for example pain-relieving devices that stimulate the spinal cord, rechargeable batteries are an increasingly attractive option, but patient non-compliance is still an issue.

For most rechargeable batteries, completely discharging them can cause damage, and reduce their charge-holding ability. Therefore, the industry standard is that rechargeable devices must be replaced after two occurrences of over-discharge.

This problem has been overcome by Quallion Zero-Volt lithium-ion batteries, which can withstand repeated cases of patient non-compliance to charging requirements, without any permanent decrease in their capacity.

Zero-Volt means batteries can be stored for long periods in a deep discharged state with no permanent capacity loss. With Zero-Volt, the charge can also be completely removed when connecting batteries to volatile systems or implanting cells inside the body.

Accountable care affects battery choices

About 50% of implantable device sales are replacements, often due to batteries reaching the end of their service life. Thus, there is little incentive for device suppliers, or anyone else in the healthcare industry, to switch to rechargeables, which require less frequent replacement.

This is changing, partly due to the USA’s Affordable Care Act (ACA) of 2010, which aims to control healthcare costs. ACA incentivises doctors, hospitals and other healthcare providers to co-ordinate healthcare delivery, to improve efficiency and reduce costs. In this ‘accountable care’ model, vertically-integrated healthcare bodies take responsibility for long-term care of a defined group of patients, shifting them away from short-term thinking.

There is also a shift away from pure financial evaluation, to a holistic view, considering social welfare and productivity. In the accountable care model, the option that minimises long-term expenditure may cost more initially, but is more likely to be in the patient’s best interests.

This change from short-term to long-term means that a rechargeable battery may be preferred to a non-rechargeable, because fewer replacement procedures are required – so, lifetime cost is lower, and the patient has to endure fewer operations.

Conclusion

Today, an accountable care approach should be the main factor when designing a medical device and choosing its power source. Simultaneously, technology improvements in rechargeable batteries have overcome many previous objections – for example, with Zero-Volt technology that withstands charging non-compliance. For any new implantable product, designers should look seriously at rechargeable batteries as their preferred energy source.