Car and truck batteries need to provide 100s of amps to get an engine started. An old car/truck battery might no longer have the power left to start a high drain engine, but it will probably still be capable of providing 100+ of watts of power, which can keep the lights on and power small devices.
You can use old car/truck batteries together with solar chargers to provide off-grid electricity. The solar chargers top up the batteries each day. An old car battery can easily provide 100 watts of electricity for several hours at a time. If your energy demands are higher, use two or more batteries.
The best part of all this is you can get old car batteries for zero cost. Garages are replacing car, van and truck batteries daily. They have to pay to recycle/dispose of these old batteries. If you ask, they should be happy to give you several batteries for free. Alternatively, old car batteries are often dropped off at household waste and recycling centres. If you swing by you will probably be able to get more than enough old batteries.
Check out the video below, explaining about using an old car battery with a solar charger to provide off-grid electricity.