rolls series 5 batteries are pretty much the best batteries for deep cycling that money can buy. My experience of them is that even if you discharge them to near 100% they will still outlast most other batteries.

The payoff is that they achieve this through extremely thick plates and so as well as being massively heavy for their rated capacities, they are also extremely expensive.

If you look after them and do not discharge them below 50% my guess is that they will outlast the vehicle. Having said this, if you understand how to look after any battery it can be made to last a lot longer than one would expect.

A cheaper solution to using expensive batteries would be to use cheaper batteries but add equipment that will assist in ensuring that your batteries are able to be fully charged, not over discharged and not over charged.

A decent battery monitor that monitors amps in and amps out with a big shunt will be able to tell you accurately what level of charge your battery is at and will enable you to cut off energy users when you reach 50% discharge. This will be enough to massively increase the lifespan of your batteries.

Getting intelligent charging devices that enable you to charge you batteries beyon dthe 70% limit that is practically reachable with a standard alternator or solar regulator, will increase the usable battery capacity and make deep discharges less common. Sterling make some cheapish battery to battery chargers that use a standard 4 stage charging cycle to get your batteries to 100% charge in less time. Using an MPPT regulator on your solar cells will optimise their power output and so you will get mroe out of them

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