Electric hospital beds and mobile patient hoists look static, but their batteries face a demanding intermittent load: several linear actuators that each draw high current for a few seconds, separated by long idle periods, plus an absolute requirement to lower a patient safely when mains power fails. Paper A of this three-part series decomposes that load, anchors it to IEC 60601-2-52 for medical beds and ISO 10535 for hoists, and explains why "cycles per charge" is the specification that actually matters.
A five-function ICU bed drives backrest, leg rest, hi-lo height, tilt and trendelenburg through 24 V linear actuators; a mobile hoist drives a lifting actuator (and often a 12 V leg-opening actuator). Actuator current follows a classic intermittent duty pattern: inrush as the motor starts, a sustained raise current that rises with patient load, regenerative energy on powered lowering, and near-zero standby. Manufacturer duty ratings make the intermittency explicit — a clinical bed control box is typically rated 10 % duty, for example a maximum of 2 minutes running in any 20-minute window, and handsets run at safety extra-low voltage with ingress protection around IPX6 for wipe-down cleaning.
IEC 60601-2-52 (the particular standard for medical beds, with the 2009 edition amended in 2015 and a restructured IEC 80601-2-52 published in 2026) requires that when external power is interrupted, critical functions — above all lowering the bed surface or backrest to a safe position, including CPR release — remain operable by backup means. Real designs reflect this: beds ship with backup packs such as two 12 V 1.3 Ah batteries, drive an audible low-voltage warning (one design beeps below roughly 16 V and silences above it on charge), while a Stryker SV2 bed specifies a 24 VDC, 10 A backup battery that activates automatically when unplugged, enabling transport and power-out operation.
For patient hoists governed by ISO 10535 (hoists for the transfer of disabled persons), the meaningful energy unit is the lifting cycle — one full raise and lower of a rated patient. Commercial products publish autonomy directly in cycles: one 24 V mobile hoist specifies 40 cycles per charge with an 8–10 hour full charge, and third-party inspection protocols require a fully charged hoist to complete at least 50 consecutive lift-and-lower operations. Crucially, several mainstream hoist families use nickel-metal hydride: Molift Partner 255 and Mover 300 carry a 26.4 V 2.6 Ah NiMH pack (22 cells), while the portable Molift Smart 150 uses a 14.4 V 2.6 Ah NiMH pack rated for roughly 500 charging cycles.
Beds and hoists are docked for most of their life, asked for short high-current bursts, and must hold charge for months between mains failures. NiMH matches that pattern: high-rate cells deliver actuator inrush without sag, float charging keeps the pack perpetually ready, the aqueous chemistry is intrinsically safe beside a patient, and gradual capacity fade gives predictable warning. Paper B sizes the pack by lift-cycle energy and compares chemistries; Paper C walks the IEC 60601-2-52 / ISO 10535 validation trail.
Weijiang Power builds high-rate NiMH cells and custom 14.4/24/26.4 V packs for bed and hoist OEMs: resistance-matched welded strings for actuator surge, NTC-supervised float charging and IEC 62133-1/UN 38.3 documentation. Send your actuator current trace, rated patient load and required lift cycles and we will size a pack that still lowers safely at end of life.
