PPL seem to think Trojan 6volts are the way to go. I just purchased two Interstate flooded cell 6 volts. I paid $360 total locally for 225 Ah @ 1.6per.
Longer:
AGM’s are maintenance free. AGM’s can be charged faster but don’t tolerate overcharging or undercharging very well which can shorten its life span. Might need to change your converter/charger for proper charging. Great for when batts can be hard to get to or need to be mounted on their side. Using more than 50% capacity before recharge can shorten their life. AGM withstand cold better and keep their charge well during storage or non-use. They are considered dual use, like a deep cycle, but also can deliver high amps quickly for starting. A cheap AGM/SLA 12v is about $1.7 per amp hour. Name brands can be much more, in the range of 5 bucks per amp hour for an Optima deep cycle marine AGM.
Flooded cell (lead acid) are best for high current draw. When properly maintained and charged will probably last the longest. But that's where some ppl balk. It does take periodic inspection and adding water to the cells that need it to make them last. A 105 amp hour 12v marine/RV Everstart (27DC XC2) from Walmart is about $.78 per at 82 dollars. These can freeze, especially if undercharged, ruining the batt.
(all above @ C20 stats)
That's just scratching the surface of battery research
GL