Ok, pack is complete -- and it works like a champ!
Sorry, no DIY pics but maybe this will help someone... But, proceed at your own risk, of course!
I cannibalized an old L&M waterbottle pack that I'd used several years ago, and was now completely dead. Figured I'd spare my weak but still functional "slimline" pack.
Opened waterbottle and removed the batteries which were joined in a 3x3 brick. Three leads from the pack to the connector - red/black/white.
Red - positive
Black - negative
White - thermistor (co-terminated with black on negative end of pack)
The thermistor is a very small copper-colored cylinder with metal leads on each end. Its job is to provide the charger with a sensing of the battery pack temperature to enable proper charge cutoff. It should be placed near center of mass of the pack, and in contact with a cell. Sorry, I didn't spec the device, These instructions assume you have an old pack to rebuild with, as you're going to need the proprietary connector anyway.
Next step was to break apart the batteries from each other. They were held with a strong adhesive but were able to be wedged apart with a pair of wirecutters. Desoldered the leads for the connector. Removed the connector from the rest of the waterbottle cap; retained plastic flanging.
The one final part that must be kept is the thermostat. A small black plastic rectangle with metal leads. It also should be near center mass and in contact with cells. Its job is to open the circuit if the pack temp gets too high. It will reset when temp drops. Hopefully it will never have to do its job, but it is your failsafe. The thermostat is used to bridge 2 cells in the pack.
Got the 4500 mAH cells as mentioned in previous post. Purchased 12 so that I might get a set of 9 well-matched cells. This is important to avoid having a weaker cell over-discharge and lead to premature pack failure.
Charged cells individually in my Vanson charger. Tight fit, but doable. Considered this a "forming charge". Not a 16-hour charge rate, but fairly slow (700 mA). Used self-discharge feature, then charged again. A lengthy process.
For each set of 4 batteries thusly charged, assembled into temporary pack, then discharged through a 35W auto lamp (approx 3 amp load). Monitored pack voltage and when it dropped to 4.00, took quick voltage of each cell while load still applied. Picked the 9 closest cells for my pack.
I had originally intended to re-assemble back into the waterbottle, for ease of construction. However, these cells are 18mm (4500mAH) vs. the original 17mm (4000mAH), and would not fit. I imagine this is why newer L&M NiMH packs were changed to the "slimline" form factor, despite their insistence of it being driven by desire to free up everyone's waterbottle cages
. Anyway, I had fat cells and would have to go the "slimline" route.
Joined pairs of cells side-by-side with hot glue on both sides of the join. Assembled 2 "4-packs" by joining these pairs end-to-end with more hot glue, having the tabs aligned and protruding. 4-packs appeared thus:
::::::: :::::::
::::::: :::::::
Soldered the adjoining tabs, slipped heat-shrink tubing over the tabs and folded to the side, against the battery.
At this point I soldered the thermostat between 2 cells at the end, and folded back into the groove that would end up on the "inside". Likewise, the thermistor and negative lead were joined to what would be the negative end, and the thermistor laid so that it would be "inside". Joined the other 4-pack to this one with hot glue. Joined the 9th cell to the resulting pack, in the middle of one of the resulting external grooves. Completed connections between ends of the pack to complete the circuit, and finally soldered the positive lead to the connector. The loose connector then joined to the end of the pack with additional layers of hot glue.
At this point, I charged the bare pack with the OEM "turbo charger". Charge proceeded as normal. Cells got slightly warm at the end and the Dt/DT termination appeared to work properly.
Ran a run-time test, with fan blowing against the light for proper cooling. run time 3 hours 25 minutes on High. Yay!! :twothumbs I would expect it to get even a bit stronger over the next several cycles, but we'll see.
Time to make the pack road-ready. To waterproof, ruggedize and rubberize, I used PlastiDip(tm) coating, found at Home Depot. I chose the black color but they had red also. I ended up with about 6 coats to get the thickness I wanted. The battery slipped from its drying rack during the last coat, so it's even a little fuglier than it would have been.
All in all I think it came out pretty well. Looks reasonable, if not "factory". It's a bit longer than the OEM "slimline" pack, due to me canibalizing the old waterbottle connector.
Everything seems in order. My only worry was about the hot glue maybe getting soft during charge, but does not seem to be happening. The charge temp seems well below that level, and our friend the thermostat will hopefully prevent any problems should it come to that.
