This is just an educated guess but the big chip would be the RTC+NVRAM (aka CMOS), the 14-pin is probably a 4000 series inverter that is wired with 32kHz crystal to provide clock for the RTC (somehow these early RTCs couldn't do it on their own or were not as energy efficient). The transistor therefore would be a part of the charging circuitry and that should be disabled with a jumper - if there even is such an option on this mobo. Some mobos have jumpers, some require a specific connection to the header for non-rechargeable external battery, some just can't deal with anything else but NiCd (I guess NiMH would work too).
If charging is disabled then the battery might also be drained while the system is powered on. Again depends on mobo in question, some have proper bypass, some do not. And yes, these early mobos do tend to pull more current so the battery will run flat faster than on more modern 386+ mobo. The take-away is: If your mobo can't have charging disabled do monitor the state of the CRs, the current is small but they will eventually start corroding (shouldn't overheat though). If there's no charging but also no bypass then the batteries will need to be changed pretty often, like in 6 months or so.
These days I go for 3x AAA holder, on wires, for 386+ and 3x AA holder for 286 mobos. Cheaper, can be detached for long term storage, lasts a long time either way, wires let you put the holder in a place where eventual battery corrosion will not spread to the mobo. So consider that if the CRs do die in half a year from now. A holder for 2 cells also works but the voltage drop due to diodes on the mobo means you can't run them as long before you get the RTC slowing down or stopping, and a holder for 4 cells will work too but some mobos will actually run the RTC too fast due to higher voltage (still in specs though with the diodes in series). 3 seems the perfect choice.
