For what it’s worth… had a gen 1 pack that showed ‘green’ immediately when charged but would show ‘red’ on the brain immediately.
Tore the pack down and separated (6) 4/5 AA nimh cells.
Put those cells on a battery analyzer.
Internal resistance (milli ohm):
152
270
420
540
650
1615
Best specs I could find say that these cells should range from 20-50 when in good shape.
Ran a few conditioning cycles and saw these numbers drop by 30-50%.
But even with this drop, the pack can’t delivery usable current.
Takeaways? There was a definite drop and corresponding increase in pack voltage as the pack was cycled. This is a known behavior of nimh chemistry, but it was nice to see it in action.
For Ni-MH packs, it is of best practice to keep them per cell in the 1.2-1.5v range during storage. Due to self-discharge, however, one must charge the battery every once and a while if they are in storage to avoid damage. Generally with all Ni-MH cells/devices I have, they are kept fully charged as much as possible while making sure to cycle them relatively often.
Slightly unrelated here, but…
I think it would be cool to see LiFePO4 cells inside Vex IQ batteries. I know the energy density of them is quite low, along with the lower nominal voltage per cell, but the cycle life would be so much longer especially in classroom environments.
What would be a more plausible modification (if Gen 2 batteries use 18650s) is switching them out for tabless cells. With some of the crazy 10 motor bots I’ve made before, voltage sag becomes quite noticeable with the current cells in them. Tabless cells in 18650 form would have no problem dumping >50 amps, on top of being 3Ah instead of 2. They would also be more suitable for 2-3c charging, easily possible through USB-C.