BigT said:
Depends on the type of battery you plan to use. AGM batteries would be OK in a closed space, but if they need to be vented, like lead-acid batteries, you'd want to make sure the gases they produce didn't build up inside the cab where you sit.
AGM batteries are Lead acid batteries, but do not offgass unless overcharged. Which requires a rather high amp charging source whose voltage regulator is seeking too high a voltage. Usually the opposite occurs, too little amperage at too little voltage. Many Variables with this. no definitive answer.
Flooded/wet batteries/ sloshing batteries are the standard least expensive capped battery which needs venting and needs to remain upright.
Consider the option of putting the batteries below the floor.
I've got my AGM battery on something similar under my Van, but I used to have2 flooded/wet batteries there for 230AH house battery capacity. and have an access hatch from above
Know any welders?
Can you fit an 11 inch tall battery without it hanging too low underneath? Flooded 6v golf cart batteries are the best deep cycle battery bang for the buck, but they are tall, and need occasional watering, more so as they age as do all wet/flooded batteries.
Really, consider what happens if the vehicle were to flip over violently with a large heavy AGM battery inside the passenger compartment. Unless seriously restrained It could turn the occupants into human mush. If a flooded/wet battery, Add liquid sulfuric acid into a rollover worst case scenario.
Flooded batteries offgass when charging. the amount they offgass depends on Several factors. they need to offgass to reach 100% state of charge in a reasonable timespan. Lead acid batteries need to be brought upto full charge as soon as possible after any depletion, as often as possible whenever depleted, for best battery longevity, but one can certainly shoot for a C rather than an A+.
There is a big difference in battery longevity when a battery only gets 90% charged compared to one which gets 100% charged.
80% charged to 100% charged, takes about 4 hours NO MATTER how powerful the charging source might be, and even if the chromed 130 alternator was recently polished.
So If your only charging source is to be the alternator, well keep the 4 hours of driving in mind when you choose how much you decide to spend on batteries and how healthy you expect to be able to keep them, and for how long. The vehicles voltage regulator plays a huge part in this 4 hour figure too. 4 hours is under ideal voltages. Few. vehicles hold ideal charging voltages required for a deeply cycled battery
Lead acid batteries can become petulant stubborn things when cycled without ever reaching full charge. This is a guarantee, the only variable is when, and how badly Murphy's law can stick it to you when the battery fails to meet your capacity needs.