Battery Theory

There are two types of batteries. Primary and Secondary. Primary batteries are non-rechargeable and must be disposed of when fully used up. These are carbon-zinc, alkaline, lithium, mercury, just to name a few. Secondary batteries are rechargeable and can be recharged numerous times before they eventually go bad. They are Nickel Cadmium (NiCad), Nickel-Metal Hydride (NiMH). These batteries come in AAA, AA, C, D sizes. The AA being the most popular. Lead acid (wet or flooded), Lead acid (gelled or SLA), Lithium Ion (LiOn), LiFePo, Nickel Iron, and a few other specialized cells for industrial operations make up other secondary cells. Button batteries are used on computer motherboards, hearing aids, small specialized electronics are mainly primary cells. They have numbers like 386, 357, A76, CR2016, CR 2032, PX76,

A battery is normally defined as a group of cells. Each type of cell has a voltage under 3 volts. Carbon-zinc and alkaline are nominally 1.5 volts. NiCad and NiMH around 1.25 volts. Lead-acid 2.1 volts. Lithium 3 volts. Cells are stacked in "series" to obtain a larger voltage. Never connect batteries in parallel unless the chemistry allows for it such as LiPo. For the sake of discussion we will focus on the secondary, AA type cell that is used in most portable battery powered equipment. Penlight flashlights, digital cameras, GPS units, CB/FRS radios, FM walkie-talkies, portable CD players, AM/FM/SW radios, mostly use AA penlight cells.

The charging process is where an external power supply is applied in some fashion to the cell(s) at a rate fast enough for convenience, but not so fast as to overheat the cell, in order to bring them up to useful purposes.

The specified charge rate for most batteries is approximately 10% of the capacity of the cell's output for approximately 8 to 10 hours. This is called C10 rate. A slower rate would be inconvenient but possible. A faster rate of charge, under controlled conditions can bring a cell up to full charge in about an hour. A cell's life is reduced if the cell overheats and "cooks out". This is the drying out of the electrolyte within the cell. Some chemistry will allow the batteries to heat up a little to balance them but this must be done with a proper smart charger that monitors the battery temperature.

Careful monitoring of the temperature by the charge controller, and the monitoring of the state of charge by the controller while charging will prolong the life of the cell. "Smart" chargers as they are referred to, do just that and they may also send pulses of power to the cell rather than a steady current flow. This has a tendency to allow the electrodes in the cell to build up a uniform "coating" on them (especially wet cells), and between pulses, monitor the batteries condition to see if the charge is "taking". Once the charge controller senses a fully charged battery, it shuts off and provides no further charging. Some controllers however, may provide a continuous "trickle" charge or maintenance pulses to keep the battery "topped off" while in the charger for extended periods of time. Other smart chargers also have a "conditioning" mode that discharges the cells completely and then charges them up to full. This is especially important for new cells that haven't been used yet. New cells are able to provide full capacity after about 8-10 cycles of charge.

There are also two theories about NiCads. One is that they can have a "memory effect". That is, if one keeps the battery fully charged without "cycling" it to full discharge (keeping it topped of or shallow discharges), it will remember that it cannot provide its full capacity and discharges in a short period of time. The other theory is that crystals form in the electrolyte if shallow charged and causes the cell to short. Hard charging till the cell gets a little hot burns the crystals out and allows for full capacity over its service life.

More battery info:

Lithium nickel rechargeable or INR Batteries use a LiNiMnCoO2 nickel-manganese-cobolt oxide (NMC) hybrid chemistry for increased energy capacity.

An IMR battery is a rechargeable lithium-Ion Manganese battery that is Round. The first letter represents the anode, the second the cathode, and the third the shape. 

These batteries differ from other li-ion rechargeable batteries in their chemical makeup. An IMR battery uses Manganese Oxide, where other types of Li-ion rechargeable uses Cobalt Oxide in their cells.

Lithium cobalt rechargeable or ICR Batteries use a LiCoO2 lithium cobolt oxide (LCO) chemistry and are well known for having high specific energy, even amongst its powerful li-ion brothers. Therefore when using an ICR, a PCB protection circuit should always be used in the final product.

For Li-ion rechargeable batteries, the most common sizes are the 18650 (18mm diameter, 65mm length), the 26650 (26mm diameter, 65mm length), and the 21700 (21mm diameter, 70mm length). Cylinders are symmetrical, have a robust mechanical form, and can be efficiently packed.

lithium ion
It lasts only two to three years after manufacturer. It is sensitive to high temperatures. If the battery is completely discharged, it can no longer be recharged again. It is relatively expensive.

Is LiFePO4 the same as lithium ion?
The lithium-iron (LiFePo4) battery has a slight edge over the Li-ion (LiCoO2) battery for safety. LiFePO4 is a nontoxic material, but LiCoO2 is hazardous in nature, so is not considered a safe material. Disposal of Li-ion battery is a big concern for the manufacturer and user.

What voltage is LiFePO4 battery?
Each LiFePO4 cell has a NOMINAL voltage of 3.3V. A fully charged LiFePO4 cell is 3.6V, and a fully depleted LiFePO4 cell is 2.5V.