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What do the reserved bits in cell status for bq78pl114 signify?

Other Parts Discussed in Thread: BQ78PL114, BQWIZARD

We have recently made a small run of 13 8Ah battery packs using the bq78pl114 gas gauge IC. We have made over 100 of these in the past, and there have been no changes to the design or software configuration for this production run. A significant number of the packs (8) have shown some odd behaviour, whereby some time after being fully charged and having a RSOC of 100%, the pack will instantaneously drop to 1% or 0% RSOC and 0% ASOC. The pack voltage is still at a good level, and discharging the pack still gives out the pack capacity, despite constantly saying a RSOC of 0%.

If the pack is connected to a charger after the instantaneous drop in RSOC, it will jump back to 100% after a minute or two.

The issue was seen only very rarely in our first run of production several years ago.

We have detected (by polling a resting, fully charged battery using BQWizard) that 2 or 3 samples before the RSOC drops, the cell status changes from 0x00C0 to 0x0040. These correspond to bits 6 and 7 of the cell status register. Bits 6 and 7 are "reserved".

Why are there reserved bits set on the cell status register?

What do they signify?

Could this be related to the issue we are seeing?

Thanks for any assistance, Peter.