Which is better battery no 5 or battery no 7?

The 5kWh energy storage battery, commonly utilizing LiFePO4 technology such as the BSLBATT 5kWh LiFePo4 battery for solar energy storage, typically comes in two variants. The rack battery, B-LFP48-100E, weighs 45kg, while the wall-mounted battery, PowerLine, weighs 50kg. The variation in weight for batteries with the same capacity is primarily attributed to differences in housing structure, Battery Management Systems (BMS), and cell composition.

The data reveals a notably high specific energy for the LiFePO4 5kWh battery, with 102.4Wh/Kg for the PowerLine and 113.8Wh/Kg for the B-LFP48-100E. This indicates the substantial amount of energy stored per kilogram in these batteries.

Conversely, the current state of charge is expressed relative to the present battery capacity. If the current capacity is 900 mAh, a 100% charge implies having 900 mAh available, not the original 1000 mAh. This aligns with the concept that "full charge" is consistently represented as 100%, even as the battery ages and its capacity diminishes over time.

It may sound logical to expect the device's battery percentage to reflect the current charge level compared to its new state. This would mean that a full charge might show as 100% when new but could be 90% after a year and potentially 80% after two years of use, never reaching 100%. However, implementing this approach could lead to confusion for most phone users.

Size of Battery no. 5 and Battery no 7 

It's intriguing to observe the diversity in battery sizes. I'm curious about the specifications for #3, #4, #6, and #8. My assumption is that #3 corresponds to the rare B-cell, and #4 to the rare A-cell, while #6 might be either the traditional No. 6 telephone battery or an N battery. I'm uncertain about #8; perhaps it's akin to a 123?

The numeric sizes harken back to a time when, in the U.S., batteries were labeled numerically based on their height in inches, at least up to #6. Batteries from #3 to #6 featured screw terminals on the top, with one in the middle and one on the side.

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#4 – Spanning 4 to 5 inches in height, sometimes oval-shaped, also known as "reserve" dry batteries.

#5 – Between 5 and 6 inches tall, the rarest and most challenging to find.

#Z – Ancestor of the modern AA battery, occasionally sold as #7 batteries.

#7 – Similar in size to a modern AAA battery.

#8 – Resembling a large AA, the precursor to the elusive B-cell battery.

#N – Essentially an N battery.

Weight and Size Analysis 

The battery sizes remain consistent across both countries. American AA-sized batteries would seamlessly fit into a Chinese device designed for that size. The sole distinction lies in their nomenclature, as in China, AA batteries are referred to as “number 5” batteries (五号电池 [wǔ hào diànchí]).

Similarities Between Battery no 5 and Battery no 7

Dry batteries, also known as voltaic batteries, have evolved into voltaic systems composed of multiple sets of circular plates arranged in pairs and stacked in a specific order. Each circular plate contains two different metal plates with a layer of cloth between them for electrical conduction. The functionality of dry batteries is derived from this principle. These batteries contain a paste-like substance, some of which may include gelatin. Consequently, their electrolyte adopts a paste-like form, and once discharged, this type of disposable battery cannot be recharged. The zinc-manganese dry cell has an electromotive force of 1.5V, requiring multiple dry batteries to power a mobile phone.

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Commonly encountered dry batteries include No. 5 and No. 7, with No. 1 and No. 2 being less frequently utilized. This battery variant finds application in devices such as wireless mice, alarm clocks, electric toys, computers, and radios. Nanfu Battery, a well-known battery company based in Fujian, is synonymous with this type of battery.

At present, Panasonic and Rimula's lithium-ion No. 5 batteries are the best non-rechargeable batteries. Rechargeable batteries are divided into nickel-cadmium, nickel-hydrogen, and lithium-ion rechargeable batteries.

Among them, lithium-ion rechargeable batteries are the best. Nickel-cadmium batteries are usually the size of AA batteries, which are older and eliminated, but they are still sold outside.

Battery no 7 

The AAA battery, also known as the triple-A battery, represents a standard size of dry cell battery commonly employed in low-drain portable electronic devices. In accordance with designations by IEC (R03), ANSI C18.1 (24), old JIS standards (UM-4), and various manufacturer and national standards contingent on cell chemistry, a zinc–carbon battery of this size is identified. The introduction of this size dates back to 1911 when The American Ever Ready Company first presented it. In China, these batteries are referred to as "#7 batteries," a nomenclature originating from the Burgess Battery Company's designation of its AAA batteries as "Number 7."

Bottom Line

The "battery wear level" or "maximum capacity" serves as a long-term metric indicating the extent of capacity loss or retention compared to the battery's original state. This estimation is derived from tracking the charge the battery can deliver from full to empty or the charge it accepts when going from empty to full in its current condition. For instance, if a new battery has a 1000 mAh capacity and its measured capacity is now 900 mAh, the "battery wear level" is 10%, reflecting a "maximum capacity" of 90% relative to its new state. Batteries are ubiquitous in our daily lives, with two of the most familiar types being the No. 5 and No. 7 ordinary batteries. These commonly used batteries typically have a nominal voltage of 1.5V when freshly purchased.

In contrast, there exists a rechargeable battery that shares the same physical form as the No. 5 and No. 7 batteries but has a nominal voltage of 1.2V. This discrepancy prompts the question: why do batteries that appear identical differ in voltage, with ordinary batteries at 1.5V and rechargeable batteries at 1.2V?

The answer lies in the materials utilized within the batteries, as the voltage of a battery is inherently determined by the specific materials incorporated into its construction.