buying secondhand tool batteries from ebay or other good/bad

[big-all]

batteries have a limited life this can be as little as 2 years useful life and as long as 5 years

from the day a battery is made it is on the downward spiral
how its used how often its used how long its between use and charges
if its been charged correctly and at the right stage off discharge
will effect its useful life

the voltage or indicator light after charging tell you very little
the older the battery the shorter the useful run time a battery can show full charge but only have 10% of the rated power/run time
other batteries will run flat in a matter off days unused even though they show 15% overvolt[18v showing 20.7v]the faster the charge rate the higher the voltage so they can boost charge to give a high reading
a good place to start is ask for the date off manufacture then assume you have lost around 20% off the power per year
yes some will far better some worse

but my suggestion is if a battery is more than 3 years old assume its around 50% capacity so worth around 20-25% the value off a new battery

[kellys_eye]

Always a risk. A rechargeable battery is made from a number of series connected cells and failure of just one of those can prevent all the others working properly. A secondhand battery, although in 'good' condition when purchased could see one of those cells fail within a very short period of time indeed.

I wouldn't chance it - unless I was buying the battery to dismantle for the cells and to repair an already dodgy battery by individual cell replacement. Not everyone can do this and it's not recommended to anyone who doesn't know what they are doing BUT it's the only way to keep a battery going other than purchasing a NEW one.

Second-hand battery???? Avoid.

[Grumbledook]

It amazes how poor battery technology still is in pretty much everything. Take the battery life in smart phones for example.

Whoever comes up with a great battery tech is going to make a lot of money ;]

[philprime]

I have brought second hand Hitachi li-lon battery's off eBay only because the price was right never had a problem them and still going strong after a year use but I agree it's always going to be a risk to what your getting

I would always steer away from old ni-cad Battery's.

There always seems to be a great deal on powertools now days I have brought new drills as its normally cheaper than replacing the battery's on there own

[alvarezbjm2]

For me, ebay batteries are 50/50

half of the time the powder is wet

[TheToolStore]

If it's not original you'take always a risk, it's cheaper at one point, that's true, If you're lucky it's made in the same factory like the original ones (happens quiet often in china).

The Li and the Ni batteries are absolutely different.
both of them built by cells (connected in series, and paraell) but the ni-cd, ni-mh ones are the "dumb one's" the only matter - if you'd like to keep it's lifetime before charging you have to discharge completely. (even if half 30 mins before end of the job tape around the trigger and left while it's going... and then charge up fully.
Otherwise -as i know it's called flah-effect - it'll remember and after a few cycle starts to get crystallize the material inside, and decreasing the capacity.
under laboratory conditions it can be fixed... but ... not cost effective :D

The Lithium ones are a bit different... they're like to be half charged, and the most ppl kills them by overcharging, or over discharging... after a decent voltage level the cell's are starting to give up :)
The lover level is -as I remember - about 2.8 3V , the over charge level is 4.2 V approx. (ideal 3.7/ cell)

For example you have a Brilliant drill with 14V drill, (2 Ah) Li batteries (the batteries inside: 3 cells in series, and 2 series in parallel, if they're used 1.Ah cells)
If you're using it until it stops, wait a few minutes and use more.. and again again.. you're on a good way towards a new pack. The Voltage level drops to the bottom level, about 3 x 2.8V = 8.6V the lower limit where the electronics cut of to protect the cells. but it's working like a soft rubber ball.. you can press in, and as you relase it's getting back to the original form, the voltage level rises a bit - because no load on it, and the electronics releases again.. and you can use until the next cut off.
there is no more power... you're just squeezing a bit more off the batt pack.. but it's damaging as well.
The situation is the same with the overcharging, just in the other direction...

So the cheap batt's what you can get - can be refurbished.. they just replacing the cells, without reprogramming the electronics (the new cell's might be different and the lifetime is significantly decreasing during the usage)
the other way just to get some cheap cells, cheap electronic... won't live so long as well.

so it's mainly depends on the luck, you get a good one or not... the question is, is it worth to get 2-3 cheap pack instead of 1 original?
btw that's a true thing ... sometimes a new item is cheaper than the battery pack itself...