Why do rechargeable batteries die?

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There are a large variety of different battery types on the market today (see Battery types) that work in slightly different ways. Some last longer than others, but all share one common theme, they don’t last forever.

Most batteries either fail in the first six months (which usually suggests a manufacturing defect unless the unit has been incorrectly used or charged) or after several years when they are often said to have died of “old age”.

In this article we’ll list the general reasons rechargeable batteries die, but you may also be interested in the more detailed articles:

Chemical build up on the plates

All batteries have two different types of plates (known as electrodes) which are separated from each other physically, but have an electrolyte substance in contact with both. What the plates are made of and what makes up the electrolyte vary by battery type, but the principle is the same.  EXAMPLE: when an appliance is connected to a battery a chemical reaction takes place between the plates where particles move through the electrolyte and create electricity.

Recharging reverses this chemical reaction so the battery can be used again.

In the case of lead acid and sealed lead acid batteries during discharge, sulfates in the electrolyte move to the plates and recharging pushes these sulfates off the plates and back into the electrolyte. In lithium-ion batteries ions move from the negative electrode (plate) to the positive electrode while recharging pushes the ions back to the negative electrode.

Unfortunately, the reversing process involved charging a battery does not work perfectly. With lead acid batteries some of the sulfates on the plates during discharge crystallize and cannot then move back into the electrolyte during charging. In Lithium-ion batteries a film builds up on both electrodes with each charge and discharge cycle which blocks the movement of ions.

As the electrodes become ever more covered in these materials their ability to be part of the chemical reaction needed to make the battery work degrades. They discharge faster and cannot recharge to the same level that they were able to when new. Eventually they are unable to charge to the point needed to power the appliance they are designed for. At this point they are regarded as ‘dead’ even though they are usually able to power appliances which require less capacity.

This rate of build up varies by battery type. Commercially available lithium-ion are seen as a better performer able to charge and discharge up to 1,000 times while at the other end of the scale Alkaline based batteries can only manage around 50 cycles.

Electrical shorting

The plates (electrodes) in a battery cannot touch each other. If they do the cell or battery immediately discharges and cannot recharge. Electrical shorting can occur in all battery types through different means.

In a lead acid battery, for example, a plate could be badly cut during production leaving a sharp edge. This may cause no immediate issue, but later due to the vibration of a vehicle it is mounted in, this defect can cut through the separator that is supposed to keep the plates apart. In lithium-ion batteries microscopic pieces of loose metal left in the unit due to poor quality manufacturing processes can move around the battery and eventually end up in a location that connects the electrodes directly to each other.

Most electrical shorts render a battery useless immediately even if it is just one cell that has shorted out and power still exists within the battery. In a car battery made up of six 2.1 volt cells the result of one cell shorting out (known as a collapsed cell) can mean the starter motor won’t operate but the dashboard will still light up.

Mechanical degradation

The chemical reactions in a battery are physical actions, this means like with all things that are on the move, there is wear and tear. The electrodes in some lithium ion batteries are known to gradually crack up over time while lead acid batteries gradually shed the active paste applied to the plates as sulfates are pushed back into the electrolyte with each recharge. This degradation of the internal components affects their ability to recharge until they reach a point when they can no longer operate the item intended.

Abuse, such as overcharging or incorrect charging, can greatly accelerate mechanical degradation.

A final note on ‘dead’ batteries

Its important to be aware that just because a battery is no longer able to power the appliance it was being used for this does not necessarily mean it is completely dead. Leaving the battery with exposed terminals that could be accidentally shorted out might still lead to potential explosions. As such, the handling of a ‘dead’ battery should be identical to that of a brand new one and a fundamental reason why shipping companies have the same strict rules for all units, no matter their condition.

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