Is it better to let a rechargeable Li-Ion battery fully discharge and empty it then recharge it with a charger or it doesn't really matter how much it is already charged while it's charging?

 

"Full" discharge is not really necessary. There is no noteable memory effect in Li-ion batteries. However for storage/shelf life, 40% charge is recomended for minimum capacity loss. Read more about it here: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Heat is also reduce capacity, and also if you exceed the 4.2V cell voltage for each recharge. It's all in the link above.

 

Here's the deal there's a guy at work that attach a ziptie to the trigger on his drill so it can fully discharge the battery before putting it on the charger. I see it as not efficient and a waste of energy emptying it out a battery to fill it back up but he said it's better for the battery to be at "zero" before charging!!!!!

 

Here's the deal there's a guy at work that attach a ziptie to the trigger on his drill so it can fully discharge the battery before putting it on the charger. I see it as not efficient and a waste of energy emptying it out a battery to fill it back up but he said it's better for the battery to be at "zero" before charging!!!!!

This used to be standard practice for NiCads to avoid "memory effect" whereby cells that are discharged repeatedly only partly (say, half discharged) and then recharged - would tend to only provide that half-charge later in life.

NiMH - they don't show the memory effect as much, so not such a big deal here.

LiIon, however - if you discharge past some voltage, which is about 3.2v on a 3.7v-nominal cell, you *will* shorten their lifespan quickly. LiIon isn't known to show a memory effect, but overcharging or over-discharging will definitely shorten their lifespan. LiIon also tends to have a somewhat fixed lifespan, regardless of whether you use them. Once they're manufactured, the clock is ticking. This varies from one cell to the next, but generally most LiIons will be pretty kaput after 2-3 years independent of the number of cycles on the battery (as long as they aren't abused).


(My qualifications: Significant usage of all of these types in R/C modeling.)

 

Great thanks for answering guys