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Re: External battery packs

Subject: Re: External battery packs
From: madl74
Date: Sun Dec 15, 2013 5:28 pm ((PST))
I use high power Duracell dry cells for preference and find then consistent=

and reliable with a long shelf life. However you won't find ampere-hour
quotes for any dry alkaline cells as this is very dependant on how they are=

used such as discharge rate, time between discharge periods, and
temperature. Don't believe sales copy and experiment to discover the workin=
life in a particular device/application.

More expensive but longer lasting, are non-rechargeable lithium cells which=

have 3V per cell rather than 1.5V and are expensive. Button cells are this=

type, but deliver little power.

Rechargeable cells are in practice Lead acid, Nickel-metal hydride, or
Lithium-ion. All can be damaged by the over-discharge of a series battery o=
cells when the weakest cell goes into reverse charge. The most robust on
discharge are lead-acid.

Lead acid
Message: 2.
Subject: 3V per cell. Heavy, normally well sealed but contain sulphuric acid and
toxic lead which also makes them a disposal problem. Two cells can power a=

6V device, but beware of other maximum permitted voltages as the charged
voltage can go up to 2.5V per cell. They need a custom charger with a
voltage limiter or they boil dry.

Message: 1.
Subject: 2V per cell. Nickel metal hydride. No toxic cadmium. Workhorse
rechargeables, environmentally friendly but of low capacity per size and
weight. Can be charged rapidly to the end voltage, but are tolerant of
extended trickle charging. They come in the same packages as alkaline dry
cells but the lower voltage can be a problem.

Message: 3.
Subject: 6V per cell. Lithium ion. Lithium even in discharged cells can generate
explosive hydrogen which can (rarely) be a fire problem when used in
aircraft as well as laptops. Mainly used in laptops and electric cars, both=

with discharge and recharge regulators to avoid over and under charging. Th=
cell voltage can be a problem, but the power/weight ratio is by far the

Hope this helps.

David Brinicombe

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