AskAboutGadgets Archive

Recharging PDA battery every night

• posted by: Mehper C. Palavuzlar on 2010-08-23
• tagged: battery-life, battery
• score: 0

My question is about my HTC HD2. It has a Li-ion battery which drains normally in two days, but under intensive usage, it hardly makes through the night.

If I recharge it every night, would it decrease the lifetime of its battery? Or should I wait till the battery power falls under some value, let's say 20%?

Answer 1529

• posted by: Broam on 2010-08-23
• score: 4

Li-Ion batteries don't really have a memory and modern intelligent charging circuits will prevent overcharging.

They really don't need to be drained like NiCd batteries needed to be.

You can have it live on the charger overnight and it shouldn't be a big deal.

Answer 1619

• posted by: Helvick on 2010-08-29
• score: 2

Li-Ion batteries have a number of key characteristics.

• Deep discharge is not good - but your device should shut down before this happens.
• They degrade over time whatever you do.
• They degrade much faster when hotter (a 100% charged battery loses 20% capacity per annum @ 25C and 35% per annum @ 40C)
• They have better life expectancy when kept at a moderate charge level (60-70% is good) and kept in a cool place (capacity degrades at about 4% per annum @ 25C at these charge levels vs 20% for a fully charged battery).
• The recharge cycle lifetime will be somewhere between 400 and 1200 cycles depending on the model.

True deep discharge generally kills a Li-Ion battery completely and a normal charger wont charge it at all if this happens. Most devices prevent deep discharge by shutting down well before this threshold is met so it isn't normally something to worry about. Coming close to this level wont degrade the battery a such so running your phone until the battery goes flat every so often isn't a major problem - but leaving it fully discharged (but not deep discharged) for any significant length of time is risky as it will degrade and might become unusable as a result.

The best strategy for keeping Li-Ion batteries in good condition for as long as possible is to keep the device as cool as you can at all times and don't fully charge the battery if you're not going to need that charge immediately. Trickle charging that keeps them close to 100% for extended periods of time is not optimal.

e.g. If your battery has a 1200mAh rating when manufactured then after a year the fully charged capacity of a battery left at 100% continually would have degraded to 780mAh while one kept at 70% would only degrade to 1150mAh. At that stage you actually have more usable charge capacity from the battery kept at 70% and the difference will become really significant over the next year. Typically a Li-ion battery that spends most of it's time fully charged and relatively warm has almost no charge capacity after 3 years.

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