How to Determine Battery Pack Size

Battery pack size

Battery packs are an invaluable way to ensure that you never find yourself without access to electricity, whether that means charging up your phone or powering your laptop. From keeping it charged up with enough juice for use or powering a device like that of the future; battery packs offer reliable solutions.

But finding the ideal mattress can be challenging. Read on to discover what factors should be taken into account before making a purchase decision.


No matter its chemistry, battery packs are constrained by physical dimensions and balancing requirements, as cells within the battery must remain within millivolts of each other to allow power to enter and leave. When charged or discharged, balancing drains away power from higher voltage blocks to bring them closer together with their neighbors.

Beginning to select battery capacity involves considering how far a range the user requires from their pack. This should then be converted to capacity in kWh by multiplying by 0.2; this provides a rough estimate of minimum pack size that allows other factors to be taken into consideration.


As part of your battery pack selection, be sure to consider its weight. Batteries are heavy objects that have only become heavier with time as industry moves towards larger and more powerful battery packs.

Tesla Model Y’s largest battery pack currently on the market weighs in at 1,700 lbs – that’s more than enough weight to power a small car like a Chevrolet Spark! As such, it stands as one of the heaviest available options on the market.

Heavy batteries are typically found in industrial applications and provide huge amounts of energy over extended periods. Common examples are lawn mowers, power tools, generators and hybrid electric vehicles (EV). Their weight also serves to offset smaller internal combustion engine motors in hybrid EVs. Incorporating all this extra hardware makes for battery packs that often weigh over one thousand pounds!


A battery pack’s voltage is determined by its number of connected cells in series, each operating over a spectrum of voltages depending on their chemistry: nickel-based cells produce 1.2V; alkaline 1.5V; silver oxide 1.6V and lead acid over 2.0V respectively. Li-ion batteries operate between 3.0V-3.9V.

Multiplying cells together increases capacity and provides voltage levels that a single cell cannot achieve, as well as making it easier to match cell chemistry with capacity for optimal performance. Single cell configurations are common among mobile phones using Li-ion cells or nickel and copper air (producing 3V), and wall clocks, wristwatches and memory backup applications often utilize single-cell configurations as well.

Most battery packs consist of several cells connected in parallel. Each cell must meet energy and power demands while also being balanced to prevent shorting between cells in series or parallel. A failing cell draws energy away from other cells, diminishing load capability; large packs usually include fuses which disconnect it to avoid an electrical short or fire.

Batteries are measured in milliampere hours (mAh). The higher their rating is, the more energy they store and therefore, how long their batteries will last. Before making decisions about size, type, or voltage of battery packs it is crucial that one understands their technology behind.

Before selecting a battery, take into account your total power needs and maximum continuous current usage; this will determine peak discharge and continuous power requirements of your pack. It is also crucial that the power source can handle its voltage requirements; otherwise modifications may need to be made to safely utilize your pack’s batteries.

Battery manufacturers usually quote gross capacity, which takes into account both cell voltage and usable capacity (i.e. the energy a battery provides when in operation). Porsche initially advertised their 93.4 kWh Taycan battery’s gross capacity as 93.4 kWh while later adding in that its usable capacity was only 792 kWh – adding further complexity by noting this difference when giving their estimates for usable capacity (79.2 kWh in this instance).


Battery capacities are measured in milliampere hours (mAh). When selecting the appropriate battery pack size for any given application, this value is of paramount importance. Both device batteries and external battery packs contain capacities measured in this way; as the higher its capacity is, the greater is its energy storage and delivery ability over time.

Actual battery capacity can vary significantly based on factors such as load profile and duration of backup power use, as well as potential cell chemistry/size choices influenced by these considerations.

Voltage of a battery is determined by both cell chemistry and number of connected cells in series, though most types can work well with multiple connected cells being joined in parallel without significant adverse side effects. As more parallel cells are added together, their combined operating voltage increases without impacting capacity or runtime.

Battery packs must be carefully balanced to achieve peak performance. Each block of cells within a pack should be within millivolts of one another so as to maximize energy transfer in and out. Specialized circuit boards monitor voltage, temperature and interconnects of all blocks as well as using a balancing function during charging to drain energy from blocks with higher voltage levels in order to bring them closer together in charge.

As well, it is necessary to consider the thermal and electrical properties of each battery cell in addition to their ageing and degradation under typical use conditions. A modular design may prove advantageous here since individual cells can be switched out if they fail or experience excessive heat or stress.

Step four in sizing a battery pack involves establishing its usable capacity based on your load profile and desired runtime. A kWh-per-day calculator may make this easier, or simply refer to each battery’s watt-hour rating on its exterior for reference.