chemistry-batteries.md

• Tesla heats up their batteries to optimal temperatures when charging. There is also this guy who believe high temperatures while charging is acceptable, but others say it is only for short periods of time. Anecdotally, this has been false for every battery I have ever owned, so make of it what you will.
• Split batteries aren't all great. The gains you get from charging twice as fast (assuming you are still under 1C), you lose in capacity in a) wasted space between the two cells, and b) when you need to step down the voltage to use it.
• A battery's Wh value is calculated using the battery's minimum voltage, around 3.7 ~ 3.85 V. A 3 Ah battery is 3 * 3.85 = 11.55 Wh.
• This guy claims that phones don't actually charge to the rated voltage anymore.
• EV car batteries are not made the same way as phone batteries. Despite both being made with lithium ion systems, the two are different grades and cannot be compared. Car batteries are oversized (charged from 30% to 80% without telling the user that) so they last at least eight years. "A battery is also negatively impacted by the pulsed load of a mobile phone rather than the DC load of an EV."
• Lithium-ion batteries swell up / bloat when you overcharge or deep-discharge them. If you are extremely lucky, a sealed glass-back device will just open itself when the non-user replaceable battery becomes a spicy pillow. If you are extremely unlucky (which is the majority of cases), the spicy pillow damages the glass back, the internals, or both, and/or sets itself on fire.
• Quick chargers that have high voltages (e.g. 9V 2A) just convert everything back to normal voltage and higher amperage (i.e. 5V 3.6A) when it reaches the battery.
• Bump charging maximises the actual charge in your battery when the battery lies about what "100%" is. The increase can be as much as 15%. It is no longer common practice since battery replaccements are prohibitively troublesome.
• Samsung phones don't fast charge when the screen is on. Also, they tell you not to discharge under 20%.
• When buying a wireless power tool, its batteries cannot be determined by just capacity and volts alone. You need to know its maximum amperage delivery, and therefore watts.
• Sodium-ion batteries are not a thing because a) sodium is bigger so the energy is less dense, and b) rogue hydrogen reacts with the manganese electrodes and damage them irreversibly.
• Charging your laptop at work from 0% to 100% every workday, then using it at home, saves you about $1 per month, assuming electricity is $0.20 per kWh, your battery capacity is maxed out at 100Wh, and charging efficiency is 50%. If your laptop battery costs $100 every two years to replace, you need to consider pound-foolishing elsewhere.
• Rated capacity is the minimum capacity when sold. Typical capacity is a marketing value for what the capacity probably will be, but is not guaranteed.
• To dispose of batteries, throw them into a big bucket of salt water, which discharges the batteries while keeping them cool. Edit: this requires you to slice open the cells, and it might not be advisable.
• SuperVOOC charges at 10V * 5A, with the trick being two batteries inside the device at 5V each, so when you charge the two at the same time, each battery charges at 5V * 5A without having to down-convert from 10V to 5V, which normally results in heat. The two batteries still provides 5V to the device though.
• But it turns out you can't just divide batteries into infinite small ones to charge infinitely quickly. Since batteries should never exceed 1C (one of its full capacity per hour), doubling the count and halving every cell's capacity still limits the C value if capacity is halved. SuperVOOC has a heat advantage, but does not magically make batteries charge faster.
• Main counterpoints about not charging your battery overnight include: misunderstanding the difference between not charging and holding a constant state of charge, claiming everyone buys another device in two years, claiming they have been charging overnight for years and nothing has yet blown up, and mixing up voltage and amperage, not knowing the entire concept has a third dependent variable: temperature.
• 3.7V and 4.2V lithium ion batteries are the same thing. They are just labelled differently.
• Rechargeable AAA lithium batteries do exist. However, they are all in the wrong voltage (3.7V).
• Deep discharges are bad too. So you are stuck between using a battery between 49% and 50%, or wherever it is when charging voltages reaches 3.92V (54%). See also: "lithium batteries undergo unwanted chemical reactions when discharged below 3V, causing their internal resistance to be permanently and significantly raised"
• Lithium-ion batteries that drop below a certain voltage (citing anywhere from 2.0V to 3.0V) will cause permanent growths that result in the aforementioned increase in internal resistance, potentially shorting the battery, and quicker self-discharge. Don't use these batteries if kept at low voltages for more than a week (if you can even find out).
• At the cost of load capacity, thermal stability, and weight, lithium battery manufacturers can raise the battery voltage using additives, which increases capacity.
• When it comes to longevity, lithium batteries are perfectly fine with the cold (0°C) except when charging, and should charge under 45°C (ideally under 30°C, but who does that), and strictly prohibited above 50°C or below 0°C.
• Li-ion battery capacities are often reported at 27°C, when the battery provides the highest capacity, not necessarily the best health.
• According to your own math in wear and tear per charging cycle, you get the most bang for your buck from your personal (3.85V nominal, 4.4V charging) Li-pol battery if you charge from 20% to 50%. (You can charge from 40% to 50% and get like 100x the cell life, but if you charge just 10% every time, you need to charge 10x as often.) Ideal is keeping a battery between 75% and 65%. If you want to use your battery like a normal person, charging from 20% to 70% isn't that bad.
• Fast chargers totally destroy your batteries. BU-401a from 2012/2017 shows bumping charge rate to anything above 1C ("one hour charge/discharge") significantly reduces total cycles, and BU-808 says anything above 4.2V harmful for cycle count as well. The ideal charging voltage is 3.92V, and cycle count is halved for every 0.1V above that.
• 65W fast charging degrades the battery by 15% in just 255 cycles but the cycles were brutal and in high heat.
• "In general, a swollen battery occurs when the battery's cells are overcharged." Overcharging oxidises the elctrolytes in the cells, turning them into gas.
• NiMH batteries can be more reliably charged when quick charged because the charger can better detect the tiny drop in voltage when charging is complete.
• NiMH batteries should be taken out of the charger shortly after charging completes.
• To charge 3Ah in an hour, calling that 1C rate, obviously takes a 3A charger.
• Making a battery pack that can both charge and discharge at the same time apparently has detrimental effects on the lifespan of the battery. WAIT: what the hell is your phone doing while charging then? WAIT 2: it might just be a way to prevent you from making the battery charge itself.
• (Not charging to the max voltage) reduces the capacity the battery stores. "As a simple guideline, every 70mV reduction in charge voltage lowers the overall capacity by 10 percent", but can be fixed any time by charging to the max voltage.
• A and B battery sizes do exist... they are just rare.
• In IEC's button cell naming, the first two digits represent the diameter floored to the nearest millimetre, and the last two digits represent the thickness of the cell. CR2032 is 20mm * 3.2mm, CR2025 is 20mm * 2.5mm, and so on. Exceptions: CR927 is 9mm * 2.7mm (the first part is only one digit long), and CR11108 is 11.6mm * 10.8mm (the second part is three digits long).
• Old batteries hit the voltage limit sooner, which appears to limit the amount of time the battery can stay in top amperage.
• Lead acid batteries follow Peukert's_law, where the capacity of the thing decreases if you try to discharge it quickly. Lithium-ion batteries do not follow this law. It is therefore not sensible to ask "how much energy a lead-acid battery can store", because it also depends on the draw current and temperature.
• Voltage while charging has been (empirically) higher than not charging, but not as much as previously expected. Over 15000 samples, charging voltage has been 50mV higher than not charging.
• A watt-hour is exactly 3600 joules.