in the case of totally “dead” batteries (voltage under 0,5V), interconnect each of them in parallel temporally before its charging with a fully-charged battery (e.g. with a paper clip)
Meltdown Issues
these products with older firmware versions (newer versions may be OK, supposedly firmware v33 reduces the shut-down threshold temperature; the version is visible during the device’s boot) and/or AC power adapters v4 (visible as Roman numeral “IV” on it in the lower right hand corner of the label on the wall side of an adapter) can cause an explosion/meltdown of batteries during charging