Two Stores, One Power Pack: Battery–Supercapacitor Hybrid Storage and the Patented Hybrid Power Pack
Abstract
Purpose. A battery is asked to hold energy for hours and to deliver or absorb bursts of power in seconds. A supercapacitor (electrochemical double-layer capacitor, EDLC) does the second job well and the first poorly. This monograph brings together, in one document, the science of pairing the two stores, the patented Hybrid Power Pack (HPP) architecture of which the author is the inventor (US 10,523,019 B2 and family), the battery management, switching and control that make the pairing work, the sizing of the capacitor for minimum weight, and the safety, standards and evidence that bear on it. It consolidates four papers by the author and adds new chapters on current division between the stores, the realisation of the claimed switches, the controller's operating states, cold operation and regenerative braking, safety, a bounded estimate of battery life, and the test record of HPP hardware.
Method. Every relation is derived from first principles or taken from a cited peer-reviewed source, datasheet or standard. Numerical results are computed from published duty cycles (WLTC Class 3b, US06, vehicle cranking measurements, rail, crane, photovoltaic and backup-power events) with every parameter stated. Each number is labelled as sourced, computed or assumed, and each design description that goes beyond the patent wording is labelled as a design realisation.
Results. When the capacitor carries the varying part of a load, battery Joule heat falls by 1 − 1/FF², where FF is the form factor (rms ÷ mean) of the load current: 53–89 % by WLTC phase and 96.7–98.7 % for engine cranking. A capacitor stores about 6 Wh/kg against about 160 Wh/kg for a lithium iron phosphate cell, but it can release its energy in about 2 s against about 2 min for a 20 Ah cell (computed at matched load), so the two stores divide a load by frequency. In a passive 12 V pair, six 2000 F cells take 76 % of a current step at its onset and cut the battery's peak current in a 400 A crank from 400 A to 186 A (computed). Sized at end of life, the lightest capacitor bank ranges from 1.44 kg of cells for 12 V cranking (bank charged to 14.0 V) to 1426 kg for a ship-to-shore crane cycle; for a battery-electric car, 30.6 kg of cells cut battery Joule heat by 26 % on WLTC and 61.6 kg by 54 % on US06. Battery heat saved is not system energy saved: on a 30 mΩ traction pack the net energy of buffering is negative, while for cranking it is positive, with break-even resistances of 0.85–5.12 mΩ, or 2.6–6.9 mΩ including the capacitor's own resistance. The claimed platform adds cell and capacitor balancing, a state-of-charge disconnect, integration on application-specific integrated circuits and five charging inputs spanning six orders of magnitude in power.
Conclusions. The pairing delivers most where the duty is peaky and the pack small: engine cranking and start–stop, pulse power, fuel-cell buffering, rail and crane peak shaving, and the fast band of photovoltaic smoothing. In electric cars its value lies in peak-power relief, voltage support and thermal headroom from a small bank rather than in energy efficiency. A defined test programme with battery-only control arms is set out to convert each derived result into a measured one.
Key results at a glance
| Quantity | Result | Basis |
|---|---|---|
| Battery Joule-heat reduction, full buffering | 1 − 1/FF²: 53–89 % by WLTC phase; 96.7–98.7 % for cranking | Derived; computed from published cycles |
| Time scale of each store at matched load | EDLC about 2 s; 20 Ah LFP cell about 2 min | Computed |
| Passive 12 V pair, 400 A crank | Battery peak current 400 A → 186 A; capacitor takes 76 % of a step at onset | Computed |
| Lightest end-of-life capacitor bank | 1.44 kg of cells (12 V cranking) to 1426 kg (ship-to-shore crane) | Computed |
| Battery-electric car | 30.6 kg of cells: −26 % battery heat on WLTC; 61.6 kg: −54 % on US06 | Computed |
| Cranking break-even battery resistance | 0.85–5.12 mΩ; 2.6–6.9 mΩ including capacitor resistance | Computed |
Contents
- Introduction
- Two stores, two physics
- Peak, rms and mean: the benefit relation, partial buffering, buffer size and the energy boundary
- Numerical evaluation: drive cycle, cranking and the reporting set
- The patented Hybrid Power Pack architecture and its switches
- The controller: capacitor switch, operating states and energy management
- The battery management system: balancing, protection and integration
- Multi-source charging: the five inputs
- Applications ranked by physics, and the evidence sector by sector
- Sizing the supercapacitor for minimum weight
- Cold operation and regenerative braking
- Self-discharge, heat and life
- Safety
- Standards
- Test evidence and the validation programme
- The patent family
- What the combination delivers: a register of benefits
- Discussion, scope and limitations
- Conclusions
How to read the numbers
Related papers by the author
- Two Stores, One Power Pack: the physics of battery–supercapacitor hybridisation — DOI 10.5281/zenodo.22958077
- The Hybrid Power Pack as a Platform: balancing, protection and multi-source charging — DOI 10.5281/zenodo.22987200
How to cite
Rohera, H. K. (2026). Two Stores, One Power Pack: Battery–Supercapacitor Hybrid Storage and the Patented Hybrid Power Pack. A Consolidated Scientific Monograph on the Physics, Architecture, Control, Battery Management, Sizing, Safety, Standards and Evidence (Version 1.0). Zenodo. https://doi.org/10.5281/zenodo.23021958