How do i test an old li-ion drill battery to see if its still ok

[jpoopdog]

Hi,

At my local tip recycling shop, they have a fair few power drills there, and batteries too. Right now i have discovered the wonders of Li-ion technology, and how awsome it is compared to NiMH ( found i could power an entire project with a single 18650, that otherwise would have needed 4xAA's).

Anyway, they have quite a few drill batteries laying about ,however, they generally charge $5 minimum for anything you buy, regardless of size shape or quantity (that said i can buy several batteries and only pay $5 all up), and generally only have like 3 batteries there at a time. Now sometimes the battery could be in good condition, only tossed because the drill messed up and other times its because they are so old or worn out they expire, they are all flat though and i need to be able to tell the difference. I have a few high power projects comming up in which i basically NEED a big fat Li-ion power pack, or a bigger heavier SLA which probably wont work out.

So my question is this, is there a quick way i can test to see how good a random Li-ion drill battery still is?

Something i can do to get a rough grip on its remaining capacity, just a quick test to see if it is still above 50% its original capacity without actually completely charging it and seeing how long it takes to discharge.

So any suggestions on what i can do to test how good the battery still is?
The project demands high energy output for cheap, though size and capacity are somewhat irrelavent, so this is my best option, i dont want to buy anything because itle cost way too much.
I also dont want to risk them bumping up my tab considerably in a gamble for potentially broken Li-ion batteries.

Please help

 

[alec_t]

Personally I would not trust any battery from a recycling tip. If Li batteries are not treated properly they are a fire hazard.

 

[MrAl]

Hi,

I agree with Alec. Li-ion's are a little more tricky than other battery types.

Also, i dont think there is any way to test the capacity^2 of an unknown cell. Note i am quoting "capacity squared" because you dont want to know just the remaining capacity, you want to know the capacity of the capacity, or in other words, you want to know what the capacity of the cell is to store and hold a charge overall. This requires charging the cell up to a full charge and then discharging it to it's lowest level.
There are ways around this but they require knowing the charge and discharge history of the cell so you'd really have to own it from brand new.

The new cells are not terribly expensive either. If you are going to pay 5 bucks for something used that costs 8 bucks new, might as well get a new one.

 

[Ian Rogers]

Ditto!!! I tried to revive my makita drill battery.... Didn't work... Bought a new one instead

 

[audioguru]

The Li-Po batteries for my electric radio-controlled airplanes can deliver extremely high current but they "wear-out" after about 500 charge-discharge cycles if they are not discharged too low and if they are stored with half-a-charge instead of a full charge.

 

[WTP Pepper]

Li-Po & Li-Ion cells are best stored with about 40% capacity. 500 discharge cycles is pretty good for such a chemistry.
Most commercial packs should have a small PCB attached to prevent over discharge but I believe many hobbyists who use such packs remove this to get higher performance on RC models.
Keep them cool under all circumstances. Heats kills these cells pretty quickly.
My Laptop battery is stored on a fridge shelf at about half capacity when not in use. Everytime I need to use it, it seems ready and gives good performance. I charge it for use then run it down a bit and put back in the fridge.
Just remember, never try and charge a Li battery if there is a chance it's frozen.

 

[jpoopdog]

uh, the batteries cost $50, if they were $8 ide have gona and bought a whole bunch of them by now.
Also, damn
from the sounds of it theres no real way to test them then, it looks like ill just have to wait until i have other stuff there i want to buy, then include the odd li-ion battery without increasing the cost overall, and get them that way.

Thanks though

 

[canadaelk]

I got 3 good18650 out of a portable 7" DVD player. It had a bad laser. The batts fit perfectly into my Skill "Super Twist" screwdrivers. Try finding those players at your recycling depot. E

 

[audioguru]

Most commercial packs should have a small PCB attached to prevent over discharge but I believe many hobbyists who use such packs remove this to get higher performance on RC models.

The one-cell and two-cells Li-Po batteries for my electric RC airplanes do not have a protection circuit attached. The airplane electronics pulses the motor so that the maximum average current is low when the battery voltage is approaching the lowest allowed voltage then cuts off the motor completely when the lowest allowed voltage is reached. The controls are still powered so the airplane can have a controlled landing.

 

[MrAl]

uh, the batteries cost $50, if they were $8 ide have gona and bought a whole bunch of them by now.
Also, damn
from the sounds of it theres no real way to test them then, it looks like ill just have to wait until i have other stuff there i want to buy, then include the odd li-ion battery without increasing the cost overall, and get them that way.

Thanks though

Oh ok thanks for clearing that up

But you could look inside one pack? You may find that the cells themselves can be replaced which should reduce cost as long as you know how to rebuild a pack.