Hi, originally this was a post on another thread that got a bit technical! It is about battery packs that fail either through low capacity or low voltage. I have the right meters and tools and electrical/electronic background etc.
I have frequently stripped relatively newish battery packs down and isolated faulty cells. With a view to putting them back together afterwards I carefully slit the covering film to expose the cells. I can then use sticky tape to re-encase the battery. The cells, if possible should be separately monitored for voltage under charging conditions, anything over 1.5 volts is bad news, 1.46 is about right.
Another cell fault is going short circuit internally i.e current flows but no voltage across the cell.
A couple of years ago I was given a 12 volt 4600mAh pack which on stripping down had 2 cells failed, I bought 2 replacement cells and soldered them in place. When taking out the faulty cell un-peal the joining strap rather than cutting through it. You then have somewhere to solder a the new cell in place. Best of course is welding but that is beyond me so I use a 75 Watt soldering iron on the basis of going in for a very quick solder joint and not heating up the cell.
Sometimes the intelligent chargers will not charge up a battery pack as the battery has been left for a while. I use any 'old type' or dumb charger to get the pack going. For example maybe half an hour on a lead acid charger to wake up the battery and then use a modern charger.
It may have gone unnoticed but as the cells are marketted with very high amp hour capacities, try checking the weight of the cell as the higher the capacity the heavier the cell. If you still use AA cells try weighing the old 500mAh cells against the latest ones. The new AA cells can also be 1 mm wider than the old ones and you may have found problems placing them in the back of an old transmitter.
A word of advice is do not buy battery packs of any sort from China. They appear to be able to print anything they want on the battery as far as capacity goes.
This includes the 18 / 650 (eighteen six fifty) cells as well I have tested and weighed and tested for capacity for myself and there are also tests on-line that bear me out on this point. However they shoot themselves in the foot when they publish the battery specification as the weight of the battery reveals the true capacity.
The eighteen six fifty cells are LiFe and 3.6 volts. (Lithium iron phosphate). The Component shop give maximum discharge rates and personally I would go with their figures. Some 18650 batteries from China are marked as 10Ah which takes some believing!
Buy from the well known shops who specialise in batteries, they are dearer but you do get what what you pay for. I have found in the past that a phone call is often welcomed with lots of advice.
regards
Roy