Battery Equivalents and Replacements

8S LiPo Battery: All About 8S Lithium Polymer Batteries

Lithium polymer (LiPo for short) batteries feature electrolyte in the form of polymer gel, hence the name. In order to increase the voltage and, thus efficiency, more cells are connected in series.

For example, when 8 LiPo cells are connected in series, 8S ("S" for connection in Series) LiPo batteries are created, which are able to provide huge amounts of power in a very short period of time. However, regardless of advances in chemistry and other technologies, 8S LiPo batteries should be handled with care.

Published: November 14, 2022.

8s lipo battery 1

8S LiPo Batteries Features and Specifications

Lithium Polymer batteries feature electrolyte in the gel form and graphic anode and cathode in the form of a Lithium Cobalt Oxide (LiCoO2) or some similar material.

Because of that, most LiPo batteries feature soft casing, although some manufacturers also offer their LiPo batteries in the hard casing - hard casing provides more uniform pressure on the LiPo cells, ensuring more uniform performances, although differences sometimes are negligible.

On average, the normal voltage of LiPo battery cells is ~3.6-3.7 volts, although some manufacturers offer batteries with a nominal cell voltage of 3.8V.

This 0.1V difference doesn't sound much, but when 8 cells are connected in series and when they provide strong currents, the difference in output power may be significant.

For example, if an 8S battery provides 100 Amps, then:

  • 8S LiPo 3.6V/cell: 28.8V x 100A = 2880 Watts
  • 8S LiPo 3.7V/cell: 29.6V x 100A = 2960 Watts
  • 8S LiPo 3.8V/cell: 30.4V x 100A = 3040 Watts

So, when the 30.4V 8S LiPo battery provides 100 Amps, it also provides 160W more than the 28.8V 8S LiPo battery and 80W more than the 29.6V 8S LiPo battery.

Note: these are nominal voltages declared by their manufacturer. Actual voltages may differ, so if possible, check the batteries' discharge charts and graphs.

The nominal capacity of the 8S LiPo batteries varies from just a few hundred mAh to large 5-6+ Ah 8S LiPo batteries.

Discharge currents are usually in the 30-80C, although there are models that are able to provide 120C currents with 240C bursts.

This allows some high-end models to provide output powers of 40kW and even more for a few seconds and 20kW practically continuously.

Note: take that "continuously" with reserve since 120C output current can be provided for 15-25 seconds, model dependant.

Because of such output power, nominal voltage, and energy density, 8S LiPo batteries are used in high-end RC toys and hobby projects, including RC ducted fan jets, RC airplanes, RC drones, robotics projects, etc.

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8S LiPo batteries come with two sets of wires, including:

  • Discharge Wires are thick and flexible wires, usually with XT-90 connector,
  • Charging Wires are much thinner and allow balance chargers to monitor, charge and balance individual cells of the 8S LiPo battery. Charging/balance wires usually come with a JST-XH connector.

When charging 8C LiPo and any other LiPo battery, the use of balance LiPo battery chargers is highly recommended.

While LiPo batteries are able to provide huge currents, they should be treated with the utmost care when charging - while some manufacturers claim that their LiPo batteries are able to accept 7-15C charging currents, with 2-5C being recommended, personally, keep the charging currents at 0.5-1.0C and never leave LiPo batteries unattended when charging. Better safe than sorry.

fireproof bag

Also, when charging, carrying, and storing LiPo batteries, the use of fireproof bags is highly recommended - such bags can withstand temperatures up to 1000°C, giving the user time to take them outside of the home or car while the fire is still small and kept within the bag.

Note: never underestimate the LiPo batteries, never treat them as toys, and always read the manuals/instructions that came with the batteries, chargers, and fireproof bags. LiPo batteries burn without the presence of oxygen, and when the oxygen is present, they can set on fire almost everything...

In order to prolong the LiPo 8S battery lifetime, it is recommended not to overcharge them and not to over-discharge them - if possible, keep them in the 10% to 90% DoD range.

Also, it is good practice to break in new batteries using a balance charger/discharger - charge them fully, and then in the first discharge cycle, discharge them down to 25% DoD, in the second cycle down to 50% DoD and in the third cycle down to 75% DoD, keeping the charging/discharging currents low.

8S LiPo Battery vs. 4S LiPo Battery

Since 8S LiPo batteries feature 8 LiPo cells connected in series, and 4S LiPo batteries feature 4 LiPo cells connected in series, that means that one 8S LiPo battery can be replaced with two 4S LiPo batteries, right? WRONG!

Each 8S LiPo battery, at least the batteries from reputable brands, feature balanced cells - the cells that feature very similar performances in terms of internal resistance and capacity.

When such an 8S battery is charged, all 8 cells are charged individually at the same voltage and are additionally balanced as a group.

When two 4S LiPo batteries of the same nominal capacity are connected in series, they do provide the nominal voltage as one 8S battery, but internally, these two 4S batteries are not as nearly similar as eight cells in the 8S battery.

When such two 4S LiPo batteries are discharged almost completely, there is always a danger of discharging one too low, damaging the cells.

So, if You need one 8S LiPo battery, don't even think of replacing it with two 4S LiPo batteries connected in series.

Long Story Short: With their high nominal voltage and strong output currents, 8S LiPo batteries are used for high-performance RC toys, drones, planes, and similar high-energy and high-power demanding applications.

Treat them with care, and they will serve You for a long time, but if mistreated, they can burst into fire, destroying everything around them. This is a serious warning.