Function of the batteries
All electrical power on the ISS is generated through the station’s solar panels, which convert sunlight into electrical energy. However, during times when the ISS goes through “orbital night,” the solar panels can no longer produce energy. As such, it is necessary for the ISS to store energy in batteries, which it can then use to power its systems during periods of darkness. Every 1.5h the ISS makes an orbit around the earth, 45 minutes of which is in sunlight. During this period, the batteries are charged by the solar panels and the batteries are discharged while feeding the station’s loads during the 45-minute period of darkness per lane.

The nickel-hydrogen (Ni-H2) batteries
The ISS has eight separate power channels in total, with each channel having three batteries – although one battery is considered a “series” of two separate battery units connected together, which actually amounts to six batteries per channel, and thus 48 batteries on ISS in total. Each of the old batteries is of the nickel-hydrogen (Ni-H2) type, which have generally always been used in space applications because of their long life, as they can withstand a large number of discharge cycles without major deterioration. In addition, Ni-H2 batteries are not susceptible to overcharging and countercurrent, giving them good safety properties.

However, one disadvantage of Ni-H2 batteries is that they are prone to “battery memory,” where the battery can lose some of its capacity if it is not fully charged and discharged during each cycle. For this reason, regular “battery conditioning” is performed on the ISS to prevent battery memory. Each of the station’s Ni-H2 batteries consists 38 individual cells (76 cells per string of two batteries), with each cell consisting of a pressure vessel containing gaseous hydrogen stored to 1,200 psi, which is generated during the charging process itself. The oldest batteries at the station are now about 10 years old and are reaching the end of their design life.

Lithium-ion (Li-ion) batteries
This means that replacement batteries are needed to maintain the ISS until its current planned retirement date of 2024. However, Ni-H2 batteries are now considered old technology, as most of the station’s systems were designed in the late 1980s and early 1990s. The ISS program has therefore decided to modernize the station’s batteries during the replacement process by switching to modern lithium-ion (Li-ion) batteries. These battery types operate through lithium ions that move between electrodes during the charging process, rather than pressurized hydrogen gas as used in Ni-H2 batteries.

As a result, Li-ion batteries are much lighter and smaller than Ni-H2 batteries because they do not require pressure vessel containers to store hydrogen gas, which means that Li-ion batteries have a very high energy density compared to Ni-H2 batteries. This has many advantages for the ISS program, because it means that only a single Li-ion battery can replace the function of two of the previous Ni-H2 batteries. This means that only half the number of Li-ion batteries (24) are needed to replace all of the station’s Ni-H2 batteries (48), which also halves the number of launches required. Li-ion batteries are also not sensitive to battery memory, so there is no need to condition the battery. However, Li-ion batteries have some drawbacks, namely the fact that they are much more sensitive to overcharging, which must be prevented through battery management and protection systems. In addition, Li-ion batteries typically have a shorter life span than Ni-H2 batteries because they cannot endure as many charge/discharge cycles before experiencing noticeable degradation. However, the ISS Li-ion batteries are designed for 60,000 cycles and a lifetime of ten years. In addition, they will include cell balancing and adjustable charge voltage technology to maximize their lifetime.

Li-ion batteries have experienced notable problems in the past, in the form of overheating and “thermal runaway.” The Li-ion batteries that will be used on the ISS, while manufactured by the same company (GS Yuasa), were designed with lessons learned from the problems, and have passed space certification tests. In particular, ISS Li-ion batteries include two schemes against thermal runaway, voltage and temperature monitoring of individual cells, circuit protection and fault isolation of individual cells, and thermal heat barriers between cell packs.

In terms of construction, each ISS Li-ion battery contains 30 individual cells, packed in a box that retains the same dimensions and mounting interfaces as previous Ni-H2 batteries, but with a significantly reduced weight (430 pounds instead of 740 pounds). A single Li-ion battery replaces the functions of two Ni-H2 batteries, but since two Ni-H2 batteries are connected in a “string” and are considered one battery, this means that adapter plates are also needed. This is to connect the single Li-ion battery to the existing connections for the unnecessary second battery in each string, thus completing the circuit.

The sizes of hearing batteries can be recognised by the sticker on the battery pack. Hearing batteries are usually packed in blisters of 6 pieces, as follows:

Application Battery Colour

5 red Mini devices in the ear canal

10 yellow Mini devices in the ear canal

13 orange Appliances behind the ear and in the auricle

312 Brown Devices in ear canal

675 blue Gears behind the ear

That depends on the type and intensity of use. In general, the large battery type 675 lasts about three weeks, while the smallest batteries (the 5 and 10) only last a few days.

There are several differences between a lithium and an alkaline battery. The most important ones are summarised below:

• Lithium batteries generally last 7 times longer than alkaline batteries.
• Alkaline batteries are usually more affordable than lithium batteries
• Lithium batteries are often used for professional purposes, while the alkaline varieties are mainly used for consumer devices such as remote controls and radios.

For those interested, you can read more about alkaline batteries and lithium batteries on our website.

Nickel cadmium batteries and nickel metal hydride batteries have some interesting differences from each other:
– Nickel metal hydride batteries have up to twice the capacity of nickel cadmium batteries.
– Nickel cadmium batteries often suffer more from the ‘memory effect’ than nickel metal hydride batteries.
– Nickel-metal hydride batteries require less maintenance and care.

The nickel metal hydride battery can be considered an improvement on the nickel cadmium battery.

The most commonly used type of batteries are alkaline batteries. Providing a lot of energy is an important feature (also at low temperatures). They are often used for devices that consume less power for a long time. Click here for more details on alkaline batteries.

The most commonly used battery is the lead-acid battery. This is because of the simple construction of the battery and a generally low price. We provide more information on this battery type, as well as brand recommendations on our lead-acid battery page.

These are a particular type of batteries that have a number of distinguishing features:

• Lithium is a good solution when high peak power is required.
• They last on average 7 times longer than alkaline batteries.
• Lithium works at temperatures of -20 to +40 degrees.

Lithium batteries are characterised by their extremely low self-discharge. The self-discharge per year is only 1% of the capacity. The voltage of this battery is exceptionally high. This information sheet lists a number of brands that produce lithium batteries and the various product variants that come with them. Lithium is a light metal with an exceptionally high capacity (3.86 Ah/gram). When lithium is mixed with other chemicals such as manganese or sulphur, the result is a battery with high energy, low weight, reduced self-discharge and the ability to perform under extreme conditions.

Applications of lithium batteries

Lithium is used in a wide range of applications, from mobile phones and microprocessors to large industrial workplaces such as in the oil and gas industry and in space.

Click here for more information on lithium batteries.

Alkaline batteries are the most commonly used type of batteries. There are a number of characteristics of this type:

• They have a low purchase price
• The alkaline batteries deliver a lot of energy even at low temperatures
• Alkaline batteries have a low self-discharge rate

Click here for more information on alkaline batteries.

A lead-acid battery is the most commonly used type of battery. Lead-acid batteries have several advantages:

• They have a simple design
• Have a generally low price
• Are suitable for various applications such as telecommunications, data centres, railways, defence and security systems

Click here for more information on lead-acid batteries.