Often the glove box light remaining on can cause this..... OH wait there's no glove box, sorry couldn't resist. Do you have a radio/stereo these take some voltage to keep things going but not enough to drain the battery in a couple of days. As suggested a new battery might be needed. Newer vehicles have an IOD fuse (ignition off draw) that the dealers pull when the vehicles are sitting on the lot, this kills power to interior lights, radio, clock, those kinds of things, but the Landrover is so simple.
1971 series 2a 88, series 3 trans, Fairey OD, owned since 1978.