Stressful work.

[paulca]

I bought a 12 cell Laptop battery brand new.  I wanted fairly decent cells.  I know they 'should' be around 2200mAh and they will be capable of 2-3amp discharge.  More than enough for my purposes.

The plan was to make 2 x 3S2P packs and keep some cells separate.

This was the second battery I have done.  The first popped right open when I slipped a screwdriver between the halves the case and twisted.  This one... was a bugger.

When the battery spat sparks at me trying to open it I kinda knew it wasn't going to be an easy one.

When it stabbed me in the thumb with a sharp tab that broke and made me bleed all over my work shirt I just got annoyed with it.

Several sparks and some smoke later I knew I could get into real trouble fast and the reason was the insulating plastic wrap on the batterys was as fragile as tissue paper.  Even trying to cut a tab loose off a positive end resulted in sparks.  It was just too easy to nick the plastic wrap and short the cells.

Lots of jumping out of my seat, growling and I gave up trying to keep them in pairs   There was simple no safe way to cut the quads into pairs without nicking the plastic and creating fireworks.  Even if I did manage to keep them in pairs, I wouldn't trust them again.

So I cut them down to singles.  I could safely cut the - end and splay the batteries apart to cut the + tabs loose.

Then made 3 of them into a pack.  Testing all my connections before inserting the batteries, thankfully revealed I had everything in order, series wired correctly with correct balance lead connections.

Then I was just putting things away and pulled the XT60 female out of it's male solder support... and... I'd soldered the male on tthe battery... AFTER wrapping it in insulating tape.  So now I had to cut the connectors and solder the correct connector onto the live battery.

I'm glad I have one more beer in the fridge.  I need it.

The pack is now being discharged so I can see if they really are 2200mAh cells.

[Cliff Matthews]

Mom told me I'd have daze like that, but didn't say how many.. 

[paulca]

Just buy those 3400mAh NCR18650B and you will be fine. At a proper price ($5~$7 each), chance of getting fake ones is fairly low.

On ebay they range from £2.99 to £10 here.  Minefield.  Obviously the 2.99 ones are fake.  I could have bought 2 of the £10 ones instead of 12 2200 in the laptop battery.

[paulca]

I had a bad maths day yesterday, they are 2600mAh as advertised.

If I buy a 12 cell laptop battery and extract 12 cells, I could in a reasonable sense sell them for £3 a cell on ebay.  Which is about the going rate for 2600mAh generic cells brand new.  Laptop battery was £12.95.  That's just over £1 a cell.

Of course I'm not going to do that as it's boring and tedious and I'll end up pushing a tab against a battery, shorting it, while it's still in it's case and not get it open to save the day... and get hurt or burn the house down or at very least make a mess and set the building fire alarm off... embarrassing.

The stress, by the way, is just about respect for how wrong it could go while dismantling a 10Ah lithium 12V battery.