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4. Do not parallel lithium polymer cells on your own. Power packs come with a 'balancer' circuit
that must be used to keep them from discharging into each other.
Basically, don't start noodling around trying to invent your own lithium polymer cell pack!
How many recharges will I get?
This completely depends on what kind of batteries are in the mintyboost and what kind of
battery is in your device. Both are energy buckets, but the size of the buckets will tell you if you
can fill one with the other.
There are few things that make a difference:
The first thing to keep in mind is that the Mintyboost converts power from low voltage to
high voltage (5V) but it is not perfect, there is charging efficiency loss. The co nversio n
efficiency can be appro ximated as 80% - it may be higher or lower but it's pretty
close.
The device battery capacity is mAh. (The mWh is not useful here, because the
charger inside is linear.) If your gadget has a 1000 mAh battery inside, that tells you the size
of the bucket you are trying to fill.
The mintybo o st battery capacity. For fairly good batteries, this is going to be about
2800 mAh.
The fact that the most AA batteries you get have their capacity specified for low-drain use
and this is high drain use. For alkalines you can probably consider the capacity to really only
be 75% of what they say it is. For NiMH, maybe 80%, and for Lithium Po lymer it's
100% (they are really good at this sort of thing).
The mintybo o st battery vo ltage. For alkalines this is 1.5, for NiMH its going to be less,
1.2V
Let's say we are using Duracell 1.5V Alkaline AA's.
First, figure out what the milliWatt-hours of the mintyboost power supply is:
mintyboost mWh = Battery vo ltage (V) * Battery capacity (mAh) * Capacity
derating
2 * 1.5V * 2850mA * 75% = 6400 mWh
This is the battery's capacity. Next we calculate the milliAmp hours the mintyboost will output at
5V:
Output mAh @ 5V = Battery mWh (mWh)/ 5 (V) * Bo o st Efficiency
6400 mWh / 5V * 80% = 1026 mAh output
This how much current it can provide, and for how long. Now divide this by the size of the
battery it's charging. Say you are charging an iPhone 3G (which has a 1200 mAh battery inside):
# of full recharges = MB o utput mAh /Device Battery Capacity
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