Please note: this text concerns Lithium-Ion batteries only.
 
HOW TO CHARGE
If a charger (power supply) comes with your product, use the original charger.
If you have a device with standard charging socket (such as micro-USB plug that goes into the device, and USB plug that goes into the charger) use chargers with approximately 0.5 to 2.0 Amperes capacity. While you can get chargers with a capacity of 5 A or more, only use them if your device was designed to be charged with this much power. Around 1 A is fortunately close to what you can expect from the majority of computer USB sockets.
Charging should take place at between 5 and 45 degrees Celsius (41 to 113 F).
It is wise to charge only where you can observe the device, so you can stop charging if overheating should occur. A smoke alarm is a good idea if you want to charge while sleeping. It is also possible to use a safety bag, sometimes known as a LiPo bag, to increase safety. You simply put your device into the bag, then seal the bag and begin charging.
 
BATTERY LIFE
The life expectancy of Li-ion batteries is 500 to 1000 recharging cycles. You can expect full capacity until you have recharged about 500 times. From 500 to 1000 recharging cycles, capacity will decrease gradually, until almost no capacity is left, and the battery will need replacing, if this is possible and economical. Life expectancy is optimal when the battery is being used between 10 and 50 degrees Celsius.
 
WHAT NOT TO DO
First, never charge too quickly! This may damage the battery, and may even be dangerous, so do not use high-capacity chargers, unless your device comes with one as standard.
There is no memory effect in Li-ion batteries, so do not treat them like old Nickel-Cadmium types (which you had to run dry regularly).
This means that you should never run Li-ion batteries completely dry. Actually, this will damage the battery. Whenever you can, keep them between 20 and 80 per cent capacity, where they perform best. However, it is better to charge the battery to 100% capacity than to run it dry.
Never charge if temperature is at freezing point or lower (0 degrees Celsius, 32 F), since this will almost certainly damage the battery. Never carry out express charging (charging with high-capacity charger) if temperature is between 0 and 5 degrees and over 45 degrees Celsius, but only use a lower-capacity charger in this temperature interval. Do not place devices in direct sunlight at all, and never charge them in direct sunlight.
Never place the device that is being charged on a sofa, rug or clothing when charging. This can cause heat to build up, which can in turn cause overheating. Always place it on a flat, hard surface, where heat can dissipate quickly.
 
 
GENERAL BATTERY INFORMATION
Most rechargeable devices use Lithium-Ion (Li-ion) polymer batteries these days.
This type has high energy density, very low memory effect and low self-discharge.
You can find them in electric cars, golf carts, power tools and other applications, besides portable headphones, telephones and loudspeakers.
Various subtypes exist that have different strengths and weaknesses, depending on the chemicals and metals used.
Batteries gradually self-discharge, even if they are not connected to anything. Usually, you can expect a self-discharge of about 2% per month when the battery is new, and this may increase somewhat with battery age and temperature.