Charging Batteries (in General C ................................................. 88

88 Hacking Electronics

NiMH LiPo Lead–Acid

Cost per mAh Weight per mAh Self-discharge Handling of full charge/ discharge cycles Handling of shallow discharge/charge

Medium Medium Low

Medium Low

High High (flat in 2–3 months) Low (6% per month) Low (4% per month) Good Good Good

Medium (regular full discharge prolongs battery life) Medium (not wellsuited to trickle charging) Good

TABLE 5-4 Characteristics of Different Battery Technologies

Table 5-4 summarizes the features of NiMH, LiPo, and lead–acid battery technologies.

If you want your project to charge a battery in place, then a LiPo or sealed lead–acid battery is probably the best choice. However, if you want the option to remove the battery and/ or use single-use batteries, then a AA battery pack is a good compromise between capacity and size.

For ultra-high-power projects, lead–acid batteries, despite being an ancient technology, still perform pretty well, just as long as you don’t have to carry them around! They are also easy to charge and are the most robust of the technologies, offering the least chance of fire or explosion.

Charging Batteries (in General)

Certain principals apply no matter what kind of battery you are charging. So read this section before reading those that follow it concerning specific battery types.

C

The letter C is used to denote the capacity of a battery in Ah or mAh. So, when people talk about charging a battery, they often talk about charging at 0.1C or C/10. Charging a battery at 0.1C means charging it at 1/10 of its capacity per hour. For example, if a battery has a capacity of 2000mAh, then charging it at 0.1C means charging it with a constant current of 200mA.