Looking at the price of a new NP-E3 battery I realized I' d rather spend this on a nice lens than an extra battery pack, but as I feel a bit naked with-out back-up I decide to take the cheap route. Replace the NMHi cells
The previous owner seems to have been a heavy smoker as there appears to be a lot of ash on the rubber UPDATE, previous owner made perfectly clear, NO ashes, this is just shredded paper as it was stored in a box filled with this stuff
OK now for the difficult part....
Edited by WebDog on Jul 27, 2004 at 09:43 PM GMT (Reason: Corrections)
Step Two:
Using a sharp and thin flat screwdriver, try to open up the case. It seems that the sides are well glued and therefore try to start at the charging connector as it is NOT glued.
but I must admit the case were already cracked when I got it
Do not despair if it cracks... this is the sort of plastic that is used in kids plastic models and therefore easy to glue!
Step three:
carefully lift the battery pack from the case, and be careful as the spring attached to the positive end is slightly jammed, you have to press the spring to release it. You should now have this in front of you : http://hem.fyristorg.com/backup/NP-E3/batt_cell.jpg
There are 10 NMHi cells size AA stacked in pairs! Nothing fancy at all....
The shiny silvery thingy you see in the middle of the battery is infact a temperature fuse, that opens up irreversible at 93 degrees celsius! If your battery is showing zero voltage it might be a good idea to check that this has not open up!
Taped on the right side you see a flat brownish thing that is the temperature sensor for the charger, a NTC-resistor (negative temperature constant) and it shows about 10 kohm in room temperature, and if you just press a finger on it it will rapidly decrease in value (mine went down to 9 kohm), If this one is not working your charger will indeed go bananas!
You are da MAN webdog...Exactly what I had suspected...So the basic cost for a replacement in the 20 dollar range is accurate (10 bucks for the batteries, 5 dollars for the sensors and 5 bucks for the case).
Step four:
With a voltmeter check the voltage of the complete battery pack, if it were just charged it should read 12.5 volt or so. If you have less than this and it is freshly charged, measure each of the 5 twin-cells (you should really do this anyway just to make sure they are still matched...) to figure out witch one that does not hold up! Most likely you have just one cell that has gone dead and need to be replaced! If the other cell-pairs are showing 2,55 volt (NOTE one NMHi cell should be 1.25-1.30 volt fully charged) or similar they should really be in good shape! You can save money by just replacing one cell or a pair or just replace all 10 cells. Note you MUST get cells with flanges, trying to solder standard AA-cells are doomed to fail
I just saw that flanged cells are sold with a capacity of 1500-1700 mAh (at my local supplier) wich is less than the non-flanged (up to 2300 mAh) but I strongly advices NOT try these! I rather have slightly less capacity than a pack that is intermittent
If you do not see any voltage at all, check the two fuses for open circuit and make sure that the NTC-resistor is functioning.
If you cannot find a faulty cell but still see very low capacity, get a 100 ohm resistor (2watt) and start to discharge the battery, Measure the voltage and see how long it takes until the voltage over the resisitor drops down to 11 volt. With 100 ohm you will have a 125 mA flowing and if the capacity of the cells are 1500 mAh, this process may well take 12 hours for fresh fully charged cells !
Once you are satisfied with the cells replace them into the case, and make sure that the springs are fastened as they should. Be wice and only spot glue the lid, there is no need to have this air tight, and you might want to do replace more cells later on! The rubber gasket is providing the protection anyway! Remount the lock and replace the two screws! Voila you got your self a "new" NP-E3 for a nickel
And now you really deserve a or two!
Dave,
to be honest, I just got the thing this monday (yesterday) it was your battery..... there is NOTHING that should prevent me from getting just as many shots from this "refurbished" battery i.e. >1000 pictures! When I'm done that is
As I told you yesterday, I have so far extracted 600 mAh and still going strong without replacing anything nor charging. This energy extracted might be less than 50 per cent of total capacity.... with this battery showing such vital signs I'll just put it all together again and do a full discharge/charge cycle and then pop int into my camera and see what will happen.
Doing the capacity test, discharging with a resistor gives a clear indication on performance and I expect to reach >1200 mAh for sure! There is just one thing that I have yet to test, transient handling. Not sure how much current my camera needs when the shutter fires, it is likely to be large transient and if any of the indiviual cells has a large ri (internal resistance) is might show up problematic, but my understanding is that if capacity is good there should not be any issues at all!
Really, what I wanted was a back up solution when/or if I forget to have my primary battery fully charged, and it does take 2-3 hours to do this.
UPDATE 1. It seems like the very high current transient when firing the shutter might be what kills the cells. NMHi is not really well suited for high current, thats why one still see NiCd cells in battery operated power-tools despite their lower capacity. Guess I have to build a 1D2 -simulator to really test those batteries
UPDATE 2: I just blasted off 80 pictures and the low batter started to flash, measured 12,05 volt under low load (120 mA). Bear in mind I have drained the battery of at least 40 percent and I did not know how good it was charged when I begun.
UPDATE, previous owner made perfectly clear, NO ashes, this is just shredded paper as it was stored in a box filled with this stuff 
)
or two!