A linken megtalalhato a magyarazat is:

I was very fortunate to find an external battery pack header on the Pine PT429 motherboard. A simple jumper (JP1) is used to disconnect the positive terminal of the battery so that an external battery can be used. This makes the replacement that much easier. I can simply remove the battery from the board, and rig up a 4-pin battery lead instead. Because the external header will not have voltage applied when the system is on – unlike the terminals for the barrel battery – I can use a cheaper, non-rechargable battery here.

Vagyis egy jumperrel levalaszthato a belso akku, hogy kulso, nem toltheto elemmel is menjen.