Try disconnecting the battery while the car is not being used, the immobiliser and alarm system will be slowly but surely draining the battery. Either that or have a freshly charged battery ready to fit as soon as you return and put the original back on charge. The best solution is to have a battery conditioner connected to the battery if you have some mains power convenient. You mention jump leads, but they are only any use if you have another car to get the jump start from. If you are unlucky you can damage your vehicle electrics [or the donor vehicle's] by using jump leads, so avoid this if you can.