Paper A showed why a feeding pump with a warming function is a heat-dominated load whose runtime is counted per bag and per shift. Paper B turns that profile into a battery specification: it builds the per-bag milliampere-hour budget, places the low-voltage alarm margin inside the calculation, compares NiMH with primary and lithium cells on the dimensions home-care and rental fleets care about, and ends with a concrete cell-configuration method.
The budget starts from average power, not peak current. A device log over a representative regimen separates the motor's step energy (step current times step duration times steps per hour), the heater's regulated average (element watts times its closed-loop duty factor), the electronics floor, display and radio (where a wireless pump exists), and alarm and beeper energy. These sum to an average wattage that is surprisingly stable for a fixed flow rate and warming setting. Multiplying by the required runtime - a full 1000 mL bag at the slowest continuous rate, or a defined eight-hour shift with warming - gives the energy target, which is divided by nominal pack voltage to reach ampere-hours. The same derating chain used across industrial backup design then applies: depth-of-discharge ceiling, end-of-life capacity retention at the declared service horizon, cold-weather correction for transport in unheated corridors or winter home visits, and the reserve that must remain when the low-battery alarm first sounds. The animated walk-through applies the chain for a representative 1.5 W average, eight-hour, 4.8 V design; the numbers are illustrative and must be replaced with measured device logs.
The low-battery threshold is a safety feature, not a fuel gauge. IEC 60601-2-24 treats delivery accuracy as essential performance, so the threshold must be chosen so that from the moment it activates, the combination of remaining capacity and voltage-under-load still guarantees: accurate delivery for a defined grace period (long enough to reach a wall outlet or swap a cartridge), a full alarm cycle at the required sound pressure, and retention of the program and volume-delivered log. A practical method is to discharge instrumented packs while logging flow error against voltage at the worst-case heater duty, identify the voltage at which step misses or flow bias first appears, and set the alarm threshold above that point by the energy the graceful transition requires. The pack's internal resistance - a function of cell choice, weld quality and age - sets how large the voltage sag is at a heater switch-on and therefore how much margin is needed; matched, low-resistance cells buy margin that no firmware change can recover.
Three power sources compete. Primary alkaline or lithium cells give ambulatory pumps long shelf life and no charger logistics, but they cannot support sustained warming economically, their internal resistance rises as they deplete, and they create recurring consumable cost and waste. Rechargeable lithium-ion offers the highest energy density, but adds a protection and management board, stricter transport rules and cost that are hard to justify in a low-cost bedside pump expected to survive years of dock cycling. NiMH is the balanced choice for dockable ward and rental fleet devices: strong pulse current for the heater and motor together, a flat voltage plateau that keeps torque and temperature control stable, intrinsic aqueous safety next to a patient, no memory effect under modern charge management, and economical cycle life measured in hundreds of charges. The animated scorecard rates the three options on five application criteria as a qualitative engineering comparison.
Most pump motors and heater elements are designed around 4.8-7.2 V, which maps naturally to four to six series NiMH cells at 1.2 V nominal; capacity is set by cell size (AA for light ambulatory duty, C or sub-C where warming dominates and an eight-hour shift is required) and by parallel strings where the ampere-hour target demands them. Welded nickel tabs with consistent pull strength, matched capacity and resistance bins, and an NTC thermistor bonded to the string are the baseline; a pack that may be user-exchanged gets a keyed, latching housing with polarity protection and no exposed contacts. Docking charge should follow a -dV/dt or dT/dt-terminated fast phase followed by a low maintenance current, with a timer backup, because pumps live half-in and half-out of the dock and must always start a shift full.
For rental fleets and home-care providers the decisive number is cost per delivered shift across the pack's life. A NiMH pack that survives 500 or more dock cycles, accepts opportunity charging without harm and swaps in seconds amortises quickly against primary-cell consumables, while avoiding the service-exchange complexity of lithium management boards. Declaring end of life at 80 percent of nameplate capacity - and proving the pump still meets its flow-accuracy and alarm-margin requirements at that point - closes the loop between battery selection and the clinical claim. Paper C sets out the validation programme that demonstrates all of it.
Weijiang Power builds matched NiMH cells and welded packs for enteral feeding pumps and fluid warmers, with resistance binning for heater-driven voltage stability, integrated thermistors for dock charge control, and IEC 61951-2, IEC 62133-1 and UN 38.3 documentation. Send your measured average-power log by flow and warming setting, the per-bag or per-shift runtime target, the low-battery grace-period requirement and the docking pattern and we will size a pack with a demonstrated alarm reserve to its declared end of life.
