I would look at a scalable lithium ion battery. These seem to be one of the popular ones and they have an agent in SA. https://www.ultrabatt.com/batteries They're not cheap but they're life expectancy is 3 or 4 times that of a lead acid battery and they're about 1/5th of the weight so you kinda get what you pay for.

Then you'd need to decide whether to use a solar panel and charge controller or the alternator on your vehicle to recharge it.