What to Specify for a Custom Lithium Battery Pack

A custom battery pack is only as good as its specification. Because a pack is built to order, there is no catalogue model to fall back on: every dimension of the pack comes from the order. An incomplete specification leads to a pack that does not fit, does not deliver the required voltage, or fails early in the field. This guide lists the items to specify, in the order a pack maker needs them.

Voltage and capacity

State the voltage the device requires and the energy budget over the required service life. Voltage decides the series arrangement: cells in series add voltage, so a 3.6V ER cell becomes 7.2V in a 2-series arrangement and 10.8V in a 3-series arrangement. Capacity decides the parallel arrangement: cells in parallel add capacity, so two 2,400 mAh cells in parallel deliver 4,800 mAh at the same voltage. The packs on this site are built around ER cells at 3.6V, with structures such as 1S1P and 2S2P, and nominal capacity from 1,200 to 19,000 mAh at category level. Your device's voltage and energy budget narrow that range to a specific structure.

Pulse requirements

State whether the device draws steady current or short, high pulses. A wireless sensor, a GPS tracker or a meter that reports over a network draws pulses during transmission, and pulses strain a lithium thionyl chloride cell, especially after long storage. If the pulse current is high or frequent, a hybrid pulse capacitor pack — an ER cell combined with a capacitor — is the better structure, because the capacitor supplies the pulse while the cell supplies long-term energy. State the pulse current, the pulse duration and the frequency, from the device's own datasheet, so the pack can be sized correctly.

Temperature, size and connectors

State the operating temperature range at the installation site. The ER-based pack category states -55 to +85 degrees Celsius, which covers most outdoor and industrial installations, but the exact requirement should still be stated. State the physical space available, including the housing dimensions and any mounting constraints, because a pack is built to fit a device, not the other way around. State the connector or lead type required, and whether the pack needs tabs, leads, a connector housing or a specific wire length.

Protection, certification and quantities

State whether the pack needs a protection circuit and what it must protect against; hybrid pulse capacitor packs on this site are stated to include a built-in protection circuit. State the certification documents required for the destination market: certification names for the pack line are UL, UN38.3, IEC62133, RoHS, MSDS, CE and ISO9001, and certificates are available upon request, but certificate numbers are not published and documents should be requested for the specific order. State the quantity and the required delivery schedule, and note that pack prices and lead times are confirmed per order.

Examples of well-specified packs

The company's own published case examples, reported as company statements, show what a complete specification looks like in practice: a custom CR123A pack for a home fire and water-damage protection system in North America, in 1S6P and 6S1P structures at 18V and 9Ah; a custom ER14505 pack for GPS asset tracking in South Africa, at 3.6V and 5,400 mAh; and a custom ER14505 pack for an IoT device in Europe, at 3.6V and 4,800 mAh combined with an LIC1020 cell. No customer names are given in those examples, and none are given here. Each example states the cell, the structure, the voltage, the capacity and the application — the minimum a pack maker needs.

Related pages: Custom Pack Guide, Primary Lithium Battery Packs, Hybrid Pulse Capacitor Packs.

Structure notation explained

Pack structures are written as series and parallel counts: the number before S is the count of cells in series, and the number after P is the count of cells in parallel. A 1S1P pack has one cell: one in series, one in parallel. A 2S2P pack has four cells: two in series, two in parallel. A 1S6P pack has six cells in parallel at the voltage of one cell. A 6S1P pack has six cells in series at the capacity of one cell. Series adds voltage, parallel adds capacity, and the combination sets both. The company's own published case example of a CR123A pack for a home fire and water-damage protection system in North America uses 1S6P and 6S1P structures at 18V and 9Ah, which shows how the same cell can serve two different electrical requirements by changing the structure alone.

When specifying a structure, state the required voltage and capacity first, and let the structure follow from them, rather than fixing a structure and hoping the voltage and capacity work out. State the physical arrangement too, where the device housing constrains it: a long, thin pack and a square pack with the same electrical structure are different products, and the pack maker needs the housing dimensions to build the right one.

Common specification gaps

Four gaps recur in custom pack orders. The first is pulse current: an order that states only average current will produce a pack that sags during transmission, because the average hides the pulse. State the pulse current, duration and frequency. The second is temperature: an order that states only room-temperature operation will produce a pack that underperforms outdoors in winter. State the full operating range. The third is certification: an order that assumes certificates are included will stall at customs or at the customer's incoming inspection. State the documents required for the destination market, and request them for the specific order. The fourth is the connector: an order that omits the connector type, wire length or polarity will produce a pack that cannot be connected. State all three. Closing those four gaps at the specification stage prevents most of the rework that delays custom pack orders.

For a buyer placing a first custom pack order, the practical next step is a sample pack: built to the full specification above, tested in the device itself under the real load and temperature. Samples are available, minimum order value is USD $500 according to the company FAQ, and lead time is confirmed per order. A sample pack test answers the questions no specification sheet can: the voltage during pulses, the fit in the housing, the connector match, and the behaviour after storage. Once the sample passes, the bulk order is a formality rather than a gamble.

One final item belongs on every custom pack order: the acceptance test. State how the delivered pack will be checked — voltage under a defined load, capacity on a sample basis, dimensional check against the housing drawing, and connector and polarity verification. Agreeing the acceptance test at order time removes ambiguity at delivery time, because both sides know what passing looks like before the packs are built. For critical applications, consider a first-article inspection: one pack built, tested and approved before the balance of the order is produced. That step costs a little time and saves far more in rework.