Vishvas's notes

Sizes

Ref - wiki
AA -1.2V rechargeable, 1.5V alkaline
- Non china brand - panasonic
AAA
CR2016
- 3V
- 90 mAh
CR 2032 - Used in motherboards.
- 3V
- 240 mAh
LR44
- 11.6 mm x 5.4 mm.
- Shelf Life: 6-8 Years.
SR69 371
- 1.5V
- Height: 0.08" (2.05mm) Diameter: 0.37" (9.5mm)
- Non china brand - Seizaiken
LR41
- Button cell for thermometers etc..
- 7.9 x 3.6 mm
- 1.5V
- Aka SR41, SR41SW, 392, 392A, 192, 384, 92A, G3, GP192, V36, V36A, V3GA, LR736 and CX42
- Desiderata
  - zero percent Hg

Refill with distilled water periodically. Specific gravity gauges are oft included with good batteries.

Old (local) batteries are purchased by weight. Old tubular battery fetched 1200 Rs in 2020.

If one battery goes down sooner than another, current may continue to be drawn from low capacity one getting it to an unsafe/ damaged condition. So, never mix dissimilar batteries.
“The weak cell holds less capacity and is discharged more quickly than their strong brothers. Going empty first causes their strong brothers to overrun their feeble sibling to the point where a high load can push the weak cell into reverse polarity. Nickel-cadmium can tolerate a reverse voltage of minus 0.2V at a few milliamps, but exceeding this will cause a permanent electrical short. On charge, the weak cell reaches full charge first, and then goes into heat-generating overcharge, while the strong brothers still accept charge and stay cool. The weak cell experiences a disadvantage on both charge and discharge; it continues to weaken until giving up the struggle.”

Cell mismatch is less critical (compared to series connection) here with regards to output voltage. But reverse polarization of the discharged battery and consequent heating can be a problem.

Charge cycles: Current li-ion cell battery packs can last WAAAAAY longer than 500 charge cycles. Even towards the end of life, the battery itself does not stop functioning - just the charge capacity drops from 100% maybe 70-80%
Aging: Li-ion cells are affected more by calendar year than charge cycles. If you were to keep an EV for 5+ years and use it very very rarely (let’s say 100 charge cycles in 5 years), you would still see the capacity drop due to calendar aging.
70% SoC = the battery is currently operating at 70% of its capacity.

Popular rechargeable batteries
When fast charging, NiMH has to be stopped earlier than NiCd to prevent damage. This means your NiCds will be safe on a NiMH charger, just not quite 100% charged when fast charging stops.