Secondary Battery Systems

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Lead Acid, Nickel-Cadmium, Nickel Metal-Hybride, Alkaline, Lithium.

Introduction

Modern technical systems such as portable computers, mobile telecommunication sets and electrical cars need light and efficient batteries.
To increase capacity, self-discharge life and cycle life, computational models and tests have to be developed. Also the testing methods in realistic cells have to be accelerated. The availability of recycling technologies should be the most important factor while developing new battery types, as some batteries contain metals which pose a potential threat to our health and environment.

More and more secondary battery systems are offered. But with increasing capacity the cycle life was decreasing. Just the new Lithium cells have better values, both in capacity and cycle life.

Capacity of rechargeable batteries (mAH)

Summary for NiCd, NiMH and Alkaline cells

Rechargeable Alkaline, NiMH and NiCd cells have nearly the same power, so the life between charges is short, it's about 20%-40% of primary Alkaline cells. The self-discharge rate cannot be ignored, it's about 1%/day for NiCd and 2-3%/day for NiMH cells. For medium time storage they don't have to be charged, as this only reduces battery life by one cycle. NiCd cells offer the high-power that is required for HEV accelerations.

Summary for Lithium cells

Lithium batteries are very new. They have 3.0-5.0 volts, so they can't be used with most standard equipment. Some new notebooks already use Lithium-Ion batteries. Their self-discharge is less than 10% per month, that's very low.

Summary for Lead Acid batteries

Lead Acid batteries are the best developed battery type, and therefore the cheapest. Like NiCds, the offer high-power output.

Summary

Rechargeable batteries have a high initial cost, but they are the cheapest over a long time period. For every battery system a special charger should be used, to get the full cycle life. Cell life is also reduced by overcharging or not fully discharching the cells, known as memory effect. On NiMH batteries overcharging has a damaging effect. With every charge/discharge cycle batteries lose a bit of their capacity. Here's the cycle life diagram of a Li-ion battery by Maxell.

All cells should be used carefully to avoid possible hazards.
Do not let the battery come into contact with metals to avoid short circuiting, as this may generate heat.
Do not deform the battery.
Do not connect or charge the battery with polarities reversed, as it may explode.
Do not use different types of batteries together.
Stop using the battery if it leaks (it smells strange).
For more safety instructions goto Maxell.

Recommendation

Lithium cells may be used in future, but they are not available everywhere up to now. We recommend using NiCd cells, as they provide the most power per dollar. Only Lead Acid batteries are cheaper, but they are too big and heavy to carry.