All four plants that GS builds lithium-ion batteries are located in Japan and the batteries supplied to the Dreamliners are made at a factory in its Kyoto headquarters. The electrical system, which the battery is embedded into, is manufactured by Thales, Europe’s biggest defense-electronics maker.
The battery charge electronics is made by Securaplane (Tuscon, Arizona), not Thales. Thales is the power storage subsystem integrator. The FAA made the announcement that the "battery did not exceed its designed voltage of 32 volts" - according to the downloaded data from the flight recorder. The issue for the safety of the battery is not only the total voltage being applied by the charger (in this case 32 Volts) but also the charge voltage at the individual cell level which must not exceed its rated amount, for the GP Yuasa cell that is 3.7 Vdc, otherwise the cell will fail and potentially burn up and explode.
Like any battery, the cells are in a series string to create, in this case, the near 30 volt capability. The internet photo of the failed pack shows 8 cells (3.7 x 8 = 29.6). If the charge voltage for the pack is 32, then the individual cell charge is 32/8 = 4 volts, less some amount of loss. Let's say that each cell is supposed to see no more than .2 volts above its rated performance as well as not exceed a particular charge rate. (You have to apply a slightly higher voltage to a cell than its voltage state in order to push the charge into it - and then stop at the rated limit.)
The charger must perform "balance charging" which means that the charger monitors the voltage of each cell in a pack and varies the charge on a per-cell basis so that all cells are brought to the same voltage. Not all cells are "alike" and their charge profiles are slightly different, meaning that the cells could get substantially "out of balance" relative to each other and a cell (or cells) might begin to see charge voltages in excess of their rating. Say, anyone of those cells "shorts" (a common failure mechanism), then the applied voltage to the remaining cells could, without individual or smart control, increase by the proportion of the lost cell to the pack. So, now we are talking about (8 x 3.9)/7 - 3.9 = .56Vdc over the nominal applied to each cell. Lead acid and Ni-Cad batteries would not care, but it may be enough to begin a catastrophic sequence of collateral cell failures over time for a Lithium-Ion battery.
Each individual cell must have protection against collateral overvoltage - not just at the pack level. That is the job of the electronics that may be embedded in each cell along with the Securaplane charger. Securaplane claims that their charger keeps track of cell imbalance as well as other faults. But I was amused that Securaplane said as of today that they were not yet "involved" in the investigation. They should have been involved from day one.
The Securaplane design needs to be gone over with a "fine tooth comb" by experts outside of Boeing's plane division and Securaplane. Boeing has folks in El Segundo that have designed such chargers for Li-ion batteries for satellites. And, separately, the battery cells (in use) need to be tested for premature failure or degradation - which means that "good" batteries of similar operational use and the same and different lots need to be examined. Further, since the other failure driver is being over-loaded (too high of a discharge rate), Boeing needs to do "use case" analyses to determine whether there is unanticipated high load conditions and how those are mitigated.