• Battery capacity: replacement batteries and the battd file
Batteries from places like eBay often don't report their real capacity to your
If the capacity reported by your battery is equal or less than what's in the battd
file then your battery will charge to the max without changing the file.
But if the reported capacity is less than the real capacity your battery will
seem to drain too fast, and then spend hours running at 1%. In that case changing
battd may fix your erratic battery indicator.
If the reported capacity is higher than what's written in battd you need to change
it, or else your battery won't charge to its full capacity.
Editing battd is not easy, and can take a lot of trial and error to get the callibration
right. See if you can find a tweaked battd file for your device on the xda forums.
• Battery life: make your smartphone last longer without dumbing it down
• Callibration: wiping the battery stats doesn't make it last longer
The battery stats file just logs how the battery is used. It's got nothing to
do with the percentage reported by your phone, and it doesn't affect charging
and discharging at all.
• Charge time: charge to 80% does NOT make your battery last longer
Charging stops automatically when the battery voltage reaches about 4.2 V and
the charge current drops to about 3% of the maximum.
Your battery never charges to 100%, so there's no need to babysit your phone to
pull the plug.
• Charge time: charging beyond 100% doesn't make much sense
When your phone or tablet says "100% charged," you can feed it some
extra juice by keeping it plugged in longer.
But don't wait for it, because the law of diminishing returns kicks in really
When you plug your phone in, it starts charging real fast, but as it gets closer
to maximum capacity the charging rate drops real quick. The tiny amount of extra
battery power from long charges is barely noticable, and definitely not worth
• Charge time: overcharging doesn't exist
Did anyone ever tell you to pull the plug when your battery indicator reaches
100% so that it doesn't overcharge? Don't believe it!
Lithium batteries have a self-protection circuit that won't let that won't let
them overcharge, no matter how long you keep 'em plugged in.
• Dead battery: put it in the freezer to kick it back to life
Sometimes a dead battery will wake from the dead at low temperature. If it's voltage
dropped too low then two or three days in the freezer can put it back to life.
Just make sure your freezer isn't too cold. At -40 C the electrolyte freezes,
and that shortens the life of your battery. A typical household freezer doesn't
go below -20 C, so it won't freeze your battery to death. Just make sure you've
sealed your battery to keep moisture out. Water will condense from the air trapped
with your battery. This corrodes the metal contacts, so seal it real tight with
saran wrap, then put it in a ziplock bag with the air squeezed out. Let your battery
warm up to room temperature before unwrapping it.
• Draining your battery doesn't kill it
If you let your battery run dry, it will self-discharge beyond repair. Yes, this
can happen in theory, but in real life you don't need to worry about it.
When your Android screams "0%" and switches itself off, your battery
isn't empty yet. Not even close.
Your battery says that it's empty when the voltage drops to a little over 3 V
(more as it gets older and the internal resistance goes up). By then you can store
it over a year at room temperature (and twice as long in the fridge) before the
protection circuit makes it commit suicide. By then your battery is so old that
you need to replace it anyway, because lithium batteries lose capacity over the
years at any charge and there's no way to stop this.
• Memory effect: it doesn't exist for lithium batteries
Some people claim you should always charge your batteries to 100%, and then drain
them completely to 0% to avoid the dreaded memory effect. They're wrong.
There was a memory effect ages ago with really old batteries. There's not a single
Android device with such outdated batteries in it.
Android phones have lithium batteries, and they don't have any memory effect.
• Storage: freezing your battery is not worth the trouble
Freezing the electrolytes kills your battery. That doesn't mean freezers are bad
for your battery. The electrolyte freezes at about -40 C, and most consumer freezers
won't go below -20 C.
If you really want to freeze your battery, make sure to keep it dry. Water will
condense from the air trapped with your battery. This corrodes the metal contacts,
so seal it real tight with saran wrap, then put it in a ziplock bag with the air
squeezed out. Let your battery warm up to room temperature before unwrapping it.
Don't expect miracles from freezing. Storing lithium batteries in the fridge instead
of at room temperature prolongs their life a lot, cooling them down further only
has a modest (often insignificant) effect.
• Storage: storing your battery in the fridge at 40% makes it live longer
Battery charge and capacity go down over time, even if it sits on a shelf doing
nothing. But at a 40% charge its capacity goes down at less than half the rate
compared to 100%, and at 4 C it deteriorates less than half as fast than at room
Half full and cold reduces degradation a lot (from up to 20% per year down to
2% per year), so storing unused batteries in the fridge is a good idea. Just make
sure you've sealed your battery to keep moisture out. Water will condense from
the air trapped with your battery. This corrodes the metal contacts, so seal it
real tight with saran wrap, then put it in a ziplock bag with the air squeezed
out. Let your battery warm up to room temperature before unwrapping it.
• Voltage and battery charge
Voltage is a rough measure for how full your battery is, but no more than that.
Voltage vs. capacity isn't linear. When you connect your charger the voltage goes
up fast, but the amount of juice (usually expressed in mAh) rises much slower.
When the voltage reaches 4.2V (this goes quickly) your battery is not fully charged
yet. It keeps charging for a while, but really slow. When you unplug your phone
the voltage drops quick first, then it slows down a lot, and then it slows some
A typical phone battery is "full" at 4.2 V and "empty at 3.2 V, but that doesn't
mean that it's half full at 3.7 V.
• Voltage: undervolting usually makes sense
Undervolting my CPU won't improve battery life by more than 2%. Someone on a forum
Yes, and he's wrong.
Some phones run at close-to-optimal voltage/clock speed combos out of the box,
but other phones are severely overvolted. The biggest gain from undervolting is
increased standby time, because your phone spends most of its time not doing very
The guy who made the 2%-claim tested it on a Nexus at 50% display brightness with
the processor working its ass off. Your phone spends most of its time doing low
power jobs, and if you drop the voltage on that your standby time goes up. If
you value battery life you'll turn the brightness of your display way below 50%
(it's way too bright for most real world conditions) which tips the scale towards
undervolting even more.