Converter/charger Upgrade

And wow only 20 bucks...

https://www.amazon.com/IOTA-Engineering-IQ4-Smart-Charger/dp/B0030G7ZHM/ref=pd_lpo_263_lp_t_4?_encoding=UTF8&psc=1&refRID=T9PKB8WSGGQSZWR8ZZB1

Yup I would go with the add on for your current convertor.

Even just the jack adapter to get the voltage up would be a help..

But the IQ thing looks good as it jumps it up to 14.8 bulk....

http://www.iotaengineering.com/dls45.htm

These guys have just about everything, and have good and rapid tech support by email.
If you are boondocking you want a 4 stage charger, they have a few models from a couple of manufactures. I used one of their Boondooker series, which has a slightly higher output voltage (14.6) which mitigates some of the voltage drop problems at higher charging rates than the other units.
If you are hard core they also have a variable voltage unit so you can dial in what you want, but use that only if you know some about charging as you could do great harm to those pricey AGMs if not used carefully, but you can also compensate for some sins of resistance in the wires.

I was noticing bestconverter.com sell this.
which makes your unit into 4 stage. 45 Amps is still not enough for two large AGMs, unless you have a small generator in which case that may be your limit and this may be an option.