The PD9245 is a good converter, but place it close to the battery(s) over short fat cabling to make sure it can do the 45 amps. I'd say 5 feet of 4awg is not overkill. Many would. In other forums many report this fat cabling was needed before the PD and other converters would go into boost mode of 14.4v. Thinner wires fooled the charger into thinking the battery was at a higher state of charge and it would do only 13.6.
I agree your battery capacity is about half, or even less than what you need. Laptops are big power consumers. Mine uses nearly 8A/h to fully recharge the battery, when turned off, and the laptop battery is probably only at 60% of capacity compared to when new.
I'm also not a fan of Optima in deep cycle applications. These Six pack/ Spiral cell batteries excel in high physical stress/ high vibration environments. A rectangular group 31 Lifeline will or Odyssey will have ~40 more amp hours to work with, and cost about the same and still be way more resistant to vibrations than any flooded battery. Don't fall for the six pack marketing. Many reports of more recently manufactured Optima's not being nearly as durable as what they grew their reputation on, a decade or more ago. Corner cutting has become prevalent in all aspects of all products, especially those which have had the time to developed good reputations with good products and now just rely on that, and clever marketing, and customer ignorance while cutting corners everywhere they can. It is the new normal. Maximum profit first and negate any deficiencies with clever marketing while finding other corners to cut. Baby needs a new diamond.
It is easier to use less electricity than to create enough to not have to worry about it.
Keep the ambient temps for the ARB as cool as possible and make sure the condenser can breathe freely. Use LED lights. Keeping a laptop fully charged will use less electricity than cycling the laptop battery and recharging it by another battery.
Charging most any battery with a high amp charger, is pretty quick from 50 to 80%. That 80 to 100% will take twice as long or longer. Reaching that true 100% weekly is important or the battery will suffer from progressive capacity loss until at some point it cannot meet your needs after a 10 days or more of not reaching 100%. It might respond well to a full 100% charge and then deliver near its full capacity after that, but more likely is that the capacity will be reduced much faster than it would be otherwise.
This progressive capacity is unnoticed by most until at some point their battery "no longer seems to take a charge". Before this point is reached most will assume their battery is just fine and proudly, yet ignorantly, state so. Those who have the tools and knowledge to monitor voltage and amp hours removed from the battery will notice the capacity loss and will not be surprised when the battery can no longer meet their needs, or when it might not be able to meet them half way through a future outing.
But in the end, batteries are just rented. Worrying about getting the most out of a battery might not be worth it, but prematurely killing it through ignorance, is to be avoided.
Always utilize all methods to keep the batteries at as high a state of charge as possible. Opportunistic charging leads to happier batteries .
Some good reading here:
http://www.usbattery.com/usb_images/charging_instruction_2011_3.pdf
But do not necessarily apply the charging algorithms to other brand batteries.
Always try and find the battery manufacturer recommendations as to bulk current and absorption and float voltages and try and find a charger which meets these specs.
If a particular battery does not have easily available recharging instructions, then I'd say to avoid that battery. While I think Deka makes a good battery, their Intimidator AGM series, rebranded and sold under other labels have little info available in this regard, and AGMs are picky and the voltages range much more across manufacturer than common knowledge would have one believe
