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Introduction

Like the most of us I've used Li-Ion batteries in many everyday devices. I also use a few LiPo Batteries in RC-airplanes. In the last years I read about their correct usage and charging. These are some of the things I learned:

  • Discharging a cell below minimum voltage kills it (capacity decreases).
  • Overcharging a cell above the maximum voltage kills it.
  • Thats why you use a balancer while loading a pack of cells in series. It balances the cells to an identical voltage level by discharging the higher-voltage-cells.
  • There's nearly no memory effect. No need to discharge before charging.
  • For long term storage charge it to 65-80%. Not less to avoid undercutting the minimum voltage. More voltage would mean more wear and ageing, because of a higher amount of chemical reactions.
  • You should wait some time after using a battery before charging it again. Which leads me to the

Question

How long should you wait after usage before charging?

For example if I use a battery powered string-trimmer or lawn-mower and the battery has gone empty (and probably quite warm) - how long should I wait before connecting it to the charger?

I guess reasons you should wait are temperature, or ongoing chemical reactions. Also I think you should wait longer if the battery had to deliver very high-current like the lawn-mower or a fast rc-airplane which will lead to higher battery temperature.

(Sidequestion: if it's about temperature would it help to put the battery in the fridge after use, to be able to charge it earlier?)

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  • \$\begingroup\$ Please provide a link or citation to the source that told you to wait between discharging and charging. \$\endgroup\$ – Elliot Alderson May 29 '18 at 19:32
  • \$\begingroup\$ Interesting that I've heard all these before, but the last one. I think it's because it is indeed about temperature and as such considered to be "common sense" kind of thing. Meaning - you do NOT have to wait if the battery is cold already. I might be wrong, though. \$\endgroup\$ – Maple May 29 '18 at 19:34
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    \$\begingroup\$ AFAIK the reason for the "wait before charging" advice is to let the cells cool back down to room temperature prior to charging (batteries heat up under significant load, or just due to the waste heat of the device they are powering). That said, I'm no chemist. \$\endgroup\$ – jms May 29 '18 at 20:06
  • \$\begingroup\$ @ElliotAlderson A friend told it to me, but its also numer 12 here: thedronegirl.com/2015/02/07/lipo-battery which says "Never charge a battery that is still warm from usage, and never use a battery that is still warm from charging." \$\endgroup\$ – Stefan I May 29 '18 at 20:56
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High or low charges on a stored lithium battery stress it, even with the battery otherwise idle. The best way to store lithium-ion or lipo is at about half charge and close to 0C (32F) without actually freezing it. Note that there's a lot of superstition about batteries, and you'll get different answers from different places, so don't be afraid to verify.

Also:

  • Charge only at room temperature
  • Use at room temperature or slightly below
  • You'll get a lot more charge cycles if you keep it between 20-80% charge.

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries is a good detailed source.

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  • \$\begingroup\$ Hi, thanks for the answer and it's very interesting, but not what I asked. My question is like how many minutes should I wait after using a device (and the battery gets warm) before putting the battery in the charger. \$\endgroup\$ – Stefan I Jun 19 '18 at 14:51
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    \$\begingroup\$ Sorry, got sidetracked by your side question. It's always best to charge the temperature around 25C, although it will warm up some from the charging current. I'd say let it sit around (preferably inside with the A/C) for maybe 15 minutes if it's warm to the touch. \$\endgroup\$ – Cristobol Polychronopolis Jun 19 '18 at 15:20

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