You may be wondering what makes an electric bike battery work. These power banks or cells can be made of many composites and materials. Over the centuries, power banks have evolved from giant, super heavy units that had to be stationary due to their cumbersome nature, to compact and lightweight energy marvels.
It is important to understand how your battery operates and what to do if issues arise. Now it is hard to find a piece of mobile technology that doesn’t use some kind of battery to power it, so Let’s dive into the inside of the most popular types of batteries used in e bikes today. We shall focus on the tested and true lead acid battery and Sealed Lead Acid (SLA) battery.
Invented by french physicist Gaston Plante in 1859, making this the oldest type of battery. Low energy-to-weight ratio and low energy-to-volume ratio, can supply high surge currents, so the cells have a large power-to-weight ratio. Low cost and proven reliability makes these batteries ideal for starting motors in automobiles that use high currents.
These are made of a lead alloy. Lead is too soft and cannot support itself, so other metals in smaller quantities are added tor stability (Antimony, Calcium, Tin and Selenium). Even though these materials assist the stability, they can cause other issues.
Tin and Antimony improves deep cycling but increases water consumption and escalates the need to equalize itself. The positive lead-calcium plate reduces discharge but has a side effect of growing from grid oxidization when being overcharged. The modern lead acid battery uses cadmium, selenium, tin and arsenic to lower the calcium and antimony contents.
Fully discharging these batteries strains the cells and permanently steals away it’s capacity. A new battery will last some time, but the fading increases once the performance goes down to half its normal capacity.
A typical lead acid will provide 200 – 300 charge / discharges. These short cycles are due to the grid corrosion on the positive electrode, depletion of the active materials and expansion of the positive plates. This is generally referred to as “aging” and can be accelerated with elevation and high discharging.
Depending on how you charge your battery, you will get different grades of performance. Low voltage charging protects the battery, but will offer poor performance and causes a build up of sulphation on the negative plate.
High voltage increases performance, but causes grid corrosion on the positive plate. Sulfation can be reversed, but corrosion damage is unfortunately permanent. Lead acid batteries must be stored at a full state of charge to maintain its life expectancy. Low charge will cause sulphation, a condition that rips away the battery performance.
Lead acid has a moderate life span and is among the best when it comes to charge retention. For example a NiCad (Nickel-Cadmium) loses up to 40% of it’s stored energy in a three month period, compared to lead acid losing this same amount in one year. The lead acid battery is superior in zero degree conditions and beats lithium ion at subzero.
SLA (Sealed Lead Acid)
SLA (Sealed Lead Acid) batteries were the next step in the 1970s. Called the first “maintenance free” battery. It is sealed but no lead acid battery can be completely sealed. To control venting during high discharge, valves were added to vent gasses when pressure builds up.
Instead of submerging the plates in liquid, the electrolyte is impregnated into a moistened separator. This is a design similar to Nickel and Lithium based systems. This makes the battery usable no matter what position the unit is placed in.
The SLA contains less electrolyte than the flooded type, AKA “acid-starved.” The most significant advantage of sealed lead acid is the ability to combine oxygen and hydrogen to create water and prevent dry out while cycling. This occurs at a moderate pressure of 0.14 bar (2psi).
The valve serves as a safety vent if the gas buildup rises. Repeated venting should be avoided as this will lead to a soon to be dry-out. The most common types of SLA is gel, also known as valve-regulated lead acid (VRLA), and absorbent glass mat (AGM).
Gel / VRLA (Valve-Regulated Lead Acid)
The gel cell contains a silica type gel that suspends the electrolyte in a paste. Smaller batteries with capacities of up to 30Ah are often called SLA. Packed in a plastic container, these batteries are used for small UPS, emergency lighting and wheelchairs.
Thanks to the low price, dependable service and low maintenance, the SLA remains the preferred choice for healthcare in hospitals and retirement homes. The larger VRLA is used as power backup for cellular towers, Internet hubs, banks, hospitals, airports and more.
AGM (Absorbent Glass Mat)
AGM suspends the electrolyte in a specially designed glass mat. This provides several advantages to lead acid systems, including faster charging and instant high load currents on demand. AGM works best as a mid-range battery with capacities of 30 to 100Ah and is less suited for large systems, such as UPS.
Commonly used as starter batteries for motorcycles, start-stop function for hybrid cars, as well as marine and RV. The capacity of AGM fades gradually due to cycling and aging. Gel on the other hand, has a dome shaped performance curve and stays in the high performance range longer but then drops suddenly towards the end of life. AGM is more expensive than flooded types, but is cheaper than gel.
Unlike the flooded, sealed lead acid batteries are designed with a low over-voltage potential to protect the battery from reaching its gas-generating potential during charge. Excess charging causes gassing, venting and subsequent water depletion and dry-out. As a result, gel and AGM also cannot be charged to it’s full potential and the charge voltage limit must be set lower than that of a flooded.
This also applies to the float charge on full charge. In regard to charging, the gel and AGM are no direct replacements for the flooded type. If no ideal charger is available for AGM with lower voltage settings, disconnect the charger after 24 hours. This prevents gassing due to a float voltage that is set too high!
The optimum operating temperature for a VRLA battery is 25°C (77°F); every 8°C (15°F) rise above this temperature threshold cuts battery life in half. Lead acid batteries are rated at a 5-hour (0.2C) and 20-hour (0.05C) discharge rate.
The battery performs best when discharged slowly; the capacity readings are substantially higher at a slower discharge than at the 1C rate. Lead acid can deliver high pulse currents of several C if done for just a few seconds. This makes the lead acid well suited as a starter battery, also known as starter-light-ignition (SLI).
This is the type of battery used in electric bikes, wheelchairs, golf cars, forklifts and more. This battery is built for maximum capacity and a high cycle count. This is achieved by making the lead plates thicker than normal ones.
Even though these batteries are designed for cycling, full discharges still induce stress and the cycle count relates to the depth-of-discharge (DoD). Deep-cycle batteries are marked in Ah or minutes of run time. The capacity is typically rated as a 5-hour and 20-hour discharge.
Here are the advantages vs disadvantages of a lead acid battery:
- Inexpensive and simple to manufacture.
- Low discharge, among the best of rechargeable batteries.
- High power, can put out high discharge currents.
- Great performance at higher and lower temperatures.
- Lower energy than lithium, poor weight-to-power ratio.
- Slow charging time, can take from 8 to 16 hours depending on size of battery.
- Must be stored fully charged to prevent sulphation.
- Limited cycle life. Repeated cycling reduced battery life.
- Flooded batteries require watering
- Flooded types cannot be transported in other configurations (Sideways, upside down, etc.)
- Made with toxic chemicals and metals.
As much as we like having batteries that are readily available, it is certain that lead acid batteries are not the economical or environmentally friendly choice.
Leave any questions or concerns in a comment below regarding Lead Acid batteries.
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