Correct treatment of rechargeable batteries (This is a LONG text!)

(and a look on the advantages and disadvantages of some types of secondary cells)
First of all there is one major problem: it is called tl;dr. This is the wrong attitude if you want to learn about this topic. (In fact, if you want to learn anything.) I tried to keep the article short and without a lot of references and background – but it is still a very long text. No chemical equations and no general theory about galvanic cells (a battery consists of one or more galvanic cells). More practical oriented and I will only cover the most important types.

This text was written entirely from my memory, things I read at various places over years and personal experience, but there is no real source I could link to, or a book or something like this. Because of this, all information comes without any warranty.
If you think I made mistakes, tell me what is wrong and why, so I can correct this.

Why did I write this text? Because I want to save resources. If batteries last longer because of good treatment, this saves the consumer money and the earth resources.

Most important: Different battery types need different treatment

Not every chemistry can be treated alike. Something that is good for one type of rechargeable battery can be “deadly” for another. With this in mind think of the old habit of applying full deep cycles from the NiCd time: It’s not good for other types. Only one advise is for good for all batteries: Store them in cool, dry and dark place.



1 Nickel based cells:

1.1 Nickel-Cadmium batteries (prohibited in most countries because of the toxic cadmium as far as I know)
They are in general robust and better than their reputation. They have a long service life of about 20 years, which means you can still find working batteries of this type. Because of this, it’s worth looking at them.
Advantages:

• High maximal current (that’s why they were still allowed for a long transition period in electrical tools like portable electric drills).
  
• Robust and forgiving; can endure deep discharge (sometimes even cell reversal) moderate overcharge and long storage without being used.
  
• Works on low temperatures, even below freezing.
  
• High cycle count (about 1000).
  
• Can be fast charged.

Disadvantages:

• Infamous “Memory Effect” in case of repeated incomplete cycles (can be cured by applying two or three full cycles).
  
• Relatively high self discharge.
  
• Much poisonous cadmium; not really a problem(in my opinion) as long as the cells are properly recycled and not simple dropped on the waste dump.
  
• Low capacity (energy density). Unusable for today’s electronics!

1.2 Nickel-metal hydrite batteries
The successor of the NiCd. I did not like them at first because they had many disadvantages compared to NiCd. But this is no longer the case. NiMH is superior in almost every way by now. Probably because the old type has been forbidden, the battery companies did some pretty good research to improve them.
In general there are two types of NiMH:

• “normal” (highest capacity)
  
• “LSD” (This has no connection to illegal drugs! Low Self Discharge)

Advantages:

• Environmentally much better (no poisonous cadmium)
  
• Higher capacity than NiCd – but still not on par with modern Li-Ion batteries.
  
• LSD type can be stored for months and is still ready for operation.
  
• Can endure occasional abuse, but to a lesser extend than the older NiCd. Easier to damage by overcharge and extreme discharge. Cell reversal is most likely “deadly”.
  
• LSD cells with low capacity can have an extreme high cycle count (3000).
  
• Can be fast charged.

Disadvantages (mostly solved until now):

• Normal type has a very high self discharge (solved with LSD)
  
• Early NiMH had a short service life of 5 years and lower cycle count (solved; current good quality cells are on par with or even better than NiCd)
  
• Still sensitive to memory effect (to a lesser extend). Also called Lazy-battery Effect. Can be cured with two or three full cycles.
  
• Early cells had a bad maximal current (solved; there are cells for very high currents).
  
• As far as I know NiMH still does not perform very good below freezing.

How to treat nickel-based batteries:

• They are mostly forgiving.
  
• Apply full cycles from time to time. But do not discharge NiMH below 0.9V per cell. Nickel batteries don’t get damaged if you occasionally charge them before full discharge. Memory effect is mostly reversible.
  
• Do not fast-charge NiMH with old NiCd chargers. The chargers try to detect a drop in voltage that occurs as soon as the cell is full and starts overcharging (different chemical reaction → ΛU cut-off). This drop exists in both types, but is smaller with NiMH. Old chargers can’t detect full charge on the new chemistry and will overcharge NiMH badly → RIP
  
• Old NiCd multi-cell chargers might apply controlled slow overcharge to the battery after the ΛU cut-off for cell-balancing. Not good for NiMH. Also the trickle charge in old chargers is too strong.
  
• Store NiCd discharged when not in use.

2. Lead-acid batteries
There are some sub-types:

• “Wet” → normal/old type; (some of these can still be opened)
  
• “gel battery” → sealed
  
• “AGM” (absorbed glass matt) → also sealed

There are differences within these types, but in general they are treated similar (out of scope for this text). Most people only use this battery type to start their combustion engine. But in the past there have been more areas of application. They are still be in use in some electric vehicles such as wheelchairs, golf-caddies, and forklifts (where the lead also servers as counterweight). Older scooters and bicycles with electric motor may still have them. Another example where lead-acid is used until today are solar-batteries and UPS (although li-ion takes over).

Advantages:

• Cheap (AGM is more expensive)
  
• Extreme high currents for a very short time → START YOUR ENGINE!!!
  
• Easy to recycle. Yes, they consist of poisonous lead and sulfuric acid. But you can easily make new batteries out of old batteries.
  
• Wet type (if not sealed) can accept almost arbitrary amount of overcharge.
  
• Charging electronics are simple.
  
• Works below freezing.
  
• Quality batteries can have a 20 year service life.

Disadvantages:

• Heavy. I mean… it’s lead. Heavy.
  
• Lead is poisonous.
  
• Very low capacity/energy density.
  
• Low amount of full cycles.
  
• Gets permanently damaged in case of deep discharge. Seriously. Don’t deep discharge lead-acid batteries.
  
• Sulfatation gradually destroys not fully charged batteries.
  
• Very slow full charging only.

How to treat lead-acid batteries:

• Keep them fully charged.
  
• I said: Keep them fully charged.
  
• Do not ever use starter batteries in cyclic use cases! Starter batteries consist of many more thin lead plates for a bigger surface (→ more current for starting the engine). You can’t replace the more expensive deep cycle battery of e.g. and electric wheelchair with a cheap starter battery. Deep cycle batteries can do 300-600 (almost) full cycles (do not deep discharge!!). Starter batteries will fail before reaching 50 full cycles. You have been warned.
  
• While you can relatively fast charge up to 80%, the remaining 20% take many hours. Fully charge as often as possible.
  
• If you use your car (combustion engine) for short distances and the battery never gets fully charged it will have a short service life.
  
• For stationary batteries (solar): Bigger is better. If your solar-battery only gets discharged 30% most of the time, it will life “forever”.
  
• Charging for cyclic use can be done (depending on the battery) with voltages of about 2.4V-2.45V per cell.
  
• Never charge a deeply discharged lead-acid when frozen. In discharged condition the electrolyte is mostly water – not acid. It freezes. Freezing a discharged lead-acid battery might damage the lead plates.
  
• Permanent trickle charge for standby-use (UPS) only at 2.3V per cell (or the battery might lose water which is bad for sealed type). Your UPS should take care of that.
  
• If the battery can be opened, you may refill demineralized water. Don’t fill to the brim, read the manual and wear safety goggles. Sulfuric acid is really dangerous for your eyes!! [Youtube]. Quote from the professor in this video: “You can’t throw away your eyes more than once!”)

Okay… And now the part, which is most important for everyday life today:

3. Lithium-ion battery (li-ion)
This is the most complex part and cannot be done to a full extend in this text. There are so many lithium-ion battery types with different advantages and disadvantages that I can’t cover them all. Impossible. Really. They have different strengths and weaknesses in terms of:

• Energy density/capacity
  
• Cycle count
  
• Service life
  
• Safety
  
• Maximal current
  
• Cost

And none of them is the ultimate battery which only has good values in all of these categories. Mostly used are lithium cobalt oxide batteries, because they offer high capacity (smartphone zombies want their device on all day long) and are cheap (maybe also because of the high demand).

Advantages:

• Highest capacity/energy density of all current rechargeable batteries.
  
• Lightweight.
  
• Depending on the chemistry: very high cycle count (no, not your typical LiCoO2)
  
• Depending on the chemistry: very long service life (no, not your typical LiCoO2)
  
• Low self discharge.
  
• Depending on the chemistry: very high currents; stable 30-40C are possible (again, not LiCoO2, not needed for mobile electronics)
  
• Can be fast charged up to about 80%.

Disadvantages:

• Depending on chemistry: Still expensive; your average li-ion is cheap nowadays.
  
• Dangerous if damaged. Search for “Li-ion thermal runaway”)
  
• Dangerous if the separator is damaged and/or too thin designed in order to maximize capacity (“Galaxy Note 7”)
  
• Consists of many chemicals. Hard to recycle/get pure materials again.
  
• Like lead-acid: Hates deep discharge. Extremely deep discharged batteries become permanently unusable.
  
• Unlike lead-acid: Hates full charge. Yes, you read that right. To maximize the service life and cycle count, it’s best to keep li-ion between 20% to 80% charge level. If the manufacturers would choose slightly lower maximal and slightly higher minimal cut-off voltages, the batteries would last significantly longer.
  
• Last 20% of charge can take up to 2 hours.
  
• Complex protection needed to make the battery safe for the end user.

How to treat lithium-ion batteries:

• The temperature is more important for this type. Do not charge li-ion when it is hot or below freezing. Both can take long and in the worst case lead to thermal runaway.
  
• Avoid frequent deep discharge. But: If your device has a “smart battery” aka “coulomb counter” or “energy meter” it may be necessary to apply a calibration every few months:
  • Fully charge
    
  • Discharge to about 3%
    
  • Fully charge
  to get accurate results from the “fuel gauge”
  
• If stored in high temperature, li-ion ages fast.
  
• If unused, do not store fully charged. Li-ion ages faster when fully charged: But do not deplete the battery for long storage. Self-discharge might destroy the cells. Store cool and dry, about 50% charged.
  
• If the protection circuit of a li-ion disabled the battery: Do not disassemble and manually recharge the cells in order to reactivate! The separator might be damaged if the voltage dropped below a certain point. This could lead to a thermal runaway. Don’t awake a sleeping li-ion(lion)!
  
• (Most devices don’t allow you to set the cut-off voltages for charge and discharge. Keeping the voltage in moderate range would greatly improve the life.)
  
• Since many devices come with non-user-replaceable battery (GRRRR!) today, the manufacturers made sure the batteries survive mostly for 2 years under sub-optimal circumstances: About 750 cycles of a smartphone 100% → 10% → 100% carried on the body, getting warm. If you keep your smartphone cool and don’t discharge below 20% frequently, the battery will have a very long life.
  
• Avoid frequent extreme fast charge (30 minutes for 80%). It’s stress for the cells. It won’t harm them if done from time to time (Tesla Supercharger on the highway but normal charge otherwise).
  
• Never use a damaged li-ion cell! Damaged not only means leaked, but also inflated/bloated. (A little expansion is normal for aging and cycling; inflated means significantly bigger than normal) If damaged, li-ion becomes a fire hazard. Wear safety gloves and goggles when removing a damaged battery. Li-ion fire can’t be extinguished with water, on the contrary: the (small) lithium part is highly reactive with water. If a small lithium battery burns, throw it on a concrete floor (if safely possible) and let it burn out if you don’t have dry(!) sand at hand.
• Don't try extinguish a gigantic li-ion battery like those electric cars.
  
• I mentioned often the fire hazard / thermal runaway. Is li-ion more dangerous than other batteries? Yes and no. It depends largely on the type of li-ion. Normal, quality batteries in our everyday electronics are quite safe with their protection circuit. But there have often been recalls of laptop or phone batteries when something in the production went wrong (tiny metal particles that could pierce the separator). And occasional fires, often falsely described as real explosions, have happened. Considering the extreme large amount of li-ion batteries in use, they can be considered pretty safe. But: If you bypass the safety measurements and overcharge li-ion they are dangerous. (And if I was more cynical, I would make some nasty joke about the Darwin Awards at this point)

EDIT: Some minor adjustments, colors and typo.