Once the weighing load profile is understood, the design problem becomes concrete: build a rechargeable source that powers a precision measurement instrument for an entire working shift on a vibrating, sometimes freezing vehicle, delivers short print and radio peaks without disturbing the analogue rail, and can be recharged hundreds of times with almost no maintenance. This second paper develops a sealed nickel-metal hydride design for onboard forklift and portable weighing indicators. It works through cell and string configuration for the 6 V and 12 V rails that dominate the market - many pallet-truck scales ship with a 6 V block offering around 60 hours of running, vehicle terminals use a 12 V, 7 Ah auxiliary battery, and wireless forklift scales use an internal 6 V, 4 Ah block for about 40 hours - and shows how the same rails are reached with series strings of nominal 1.2 V NiMH cells. It sizes energy from the excitation-and-conversion baseline with a separate allowance for burst power, specifies the charging and protection approach that continuous readiness demands, and places NiMH candidly beside sealed lead-acid, the incumbent, and lithium chemistries so the instrument designer chooses by quantified duty rather than habit. The goal is not to claim NiMH wins every scale, but to show where it is the most defensible drop-in upgrade for a mobile, legal-for-trade instrument.
Mobile weighing instruments are organised around a handful of de-facto rails: 6 V in compact pallet-truck and handheld scales, 12 V in vehicle and floor-scale indicators, with the instrument deriving its logic and excitation rails through internal regulators. A NiMH pack reaches these rails by series-connecting nominal 1.2 V cells - five cells for a 6 V-class source, ten for 12 V - with the end-of-charge and end-of-discharge envelope matched to the indicator's regulator input so the legal-metrology low-voltage boundary is reached only after the instrument has raised its alarm and closed any open transaction.
Because every series cell must share charge and discharge, the pack uses matched, lot-consistent cells, welded tabs and a robust carrier that resists forklift vibration; longer strings add cell-level monitoring that feeds a fuel-gauge and the instrument's low-battery warning. Paralleled strings raise capacity for multi-shift operation without raising voltage, and keyed, polarised connectors prevent a service technician from fitting a pack the wrong way round on a busy loading dock.
Capacity is sized from two separate requirements. The energy budget integrates the continuous bridge-excitation and conversion current, the display duty cycle set by the energy-saving menu, and the expected number of print or wireless transactions over the longest shift; the power budget checks that the pack's internal resistance can supply the thermal-printer or radio transmit peak while holding the analogue rail above its minimum. Published reference points - roughly 60 hours from a 6 V pallet-truck battery, about 40 hours of indicator running from a 6 V, 4 Ah block, and a 12 V, 7 Ah auxiliary in a vehicle terminal - let the designer anchor the calculation in real instruments rather than optimistic cell datasheets.
A derating for low temperature and for end-of-life capacity is applied so the shift-long promise holds in a cold store and after several hundred cycles; the first animated figure steps through this sizing flow. Separating the energy and power calculations is what prevents the common failure of a pack whose average-current arithmetic is correct but whose voltage collapses during a label print, corrupting the very reading being printed.
Sealed lead-acid is the incumbent in onboard scales because it is cheap and familiar in 6 V and 12 V blocks, but it is heavy, loses substantial capacity after cold soak, suffers under partial-state-of-charge cycling, and its internal resistance climbs as it ages - so a block that once ran two shifts slowly runs less than one. Sealed NiMH offers roughly double the specific energy, a flatter high-rate behaviour in the cold, no free acid and no sulphation, and it tolerates the shallow, daily cycling a forklift scale actually imposes.
As a drop-in upgrade, a 5S or 10S NiMH pack can occupy the same bay and feed the same charger architecture with a charge profile suited to NiMH termination (-delta-V or peak-voltage detection with temperature and timer backstops, and a low maintenance current in the cradle). The instrument gains lighter weight - meaningful on a manually pushed pallet truck - and more predictable runtime through the shift, while avoiding lithium's cold-charge restriction and more elaborate protection.
A forklift scale battery spends its working life in daily cycles - discharged through a shift, recharged in a dock or vehicle cradle overnight - so the charger, not the discharge, dominates long-term reliability. NiMH is charged with a controlled current terminated by -delta-V or peak detection, backed by a thermistor cut-off and a safety timer, and held ready with a low maintenance current rather than a hard constant-voltage float that would overcharge and age the cells. A smart cradle can top the pack opportunistically between shifts without harming it.
The same thermistor and a fuel-gauge based on voltage and coulomb counting expose state-of-charge to the indicator, which is how a legal-for-trade instrument gives the operator an honest low-battery warning well before the metrological boundary. Because sealed NiMH contains no liquid electrolyte, the pack needs no watering, no acid-spill containment and no upright mounting constraint, simplifying installation on a tilting forklift mast.
Lithium iron phosphate and other lithium chemistries give high energy density and long cycle life, but require a battery management system for balancing and protection, must not be charged below freezing - a real limitation in cold-store operation - and carry more involved transport considerations. Disposable primary cells avoid a charger but are expensive in ongoing cost and waste over a fleet of daily-used scales, and their voltage decay gives little warning. Sealed lead-acid remains cheapest up front but is heavy, cold-weak and maintenance-sensitive.
Sealed NiMH occupies the middle that suits a mobile, repeatedly cycled, sometimes cold instrument: far lighter and more cold-tolerant than lead-acid, simpler and more cold-forgiving than lithium, and rechargeable in contrast to primaries. The second animated figure scores the candidate chemistries on the axes that matter for an onboard scale; for a single-shift or multi-shift legal-for-trade instrument that is charged in a cradle every night, NiMH is frequently the most robust total-cost choice, while a permanently float-charged fixed platform scale or an ultra-light handheld may legitimately favour another chemistry.
Before integration the design is validated against the real duty on the bench: an electronic load replays the measured excitation baseline with superimposed printer and radio bursts while the pack is hot-soaked and cold-soaked; runtime is measured to the instrument's own low-battery and metrological cut-off points rather than to an arbitrary cell voltage; cycle runs confirm capacity and internal resistance stay within bounds across the service interval; and vibration testing reproduces forklift mast and floor spectra to check tab and weld integrity.
Passing that programme yields a characterised pack with a documented runtime-versus-temperature curve, a guaranteed burst capability and a predicted cycle life - the foundation for the standards and type-approval campaign the final paper describes, and the evidence an OEM needs to specify NiMH with confidence in a legal-for-trade weighing product.
Weijiang Power designs and manufactures sealed nickel-metal hydride cells and matched industrial packs for remote, off-grid and safety-related equipment, and supports OEM partners with IEC 61951-2 performance files, IEC 62133-2 safety evidence, pulse-load characterisation, wide-temperature testing and charger/pack co-validation. Tell us your duty cycle, peak current, temperature envelope, autonomy target and the standards your product must meet, and our engineers will specify a cell-and-pack combination that protects runtime, reliability and service life. Review the range on the products page.
