From their website:
"I want to use this product to charge cell phones, ipods and related devices. Can I utilize alkaline batteries in a pinch if I'm on a plane for and extended period and the NiMH batteries are depleted? I understand that I cannot recharge alkaline batteries.
A:
No, the Guide 10 Plus is set up specifically for NiMh batteries. You can use any replacement NiMh batteries, but alkaline batteries can damage your unit."
So if you have a stash of charged NiMH batteries you could keep reloading it. The Goal Zero battery unit is designed to be used with one of their small solar panels to recharge the batteries and/or your device in the field but they do sell just the battery unit seperatly and it recharges via USB input. For recharging the inReach, you can use any battery or power supply you might use for charging other devices with USB power input, Delorme just seems to have partnered with Goal Zero. I have a Goal Zero but usually take a different battery for recharging stuff for one reason or another. Unlike my cell phone, I've not had to recharge the inReach in the field (yet). However, I mostly use it for weekend or day trips. Using a solar panel just complicates matters, perhaps if on a really long trip or at a base camp.
Someone does make a unit you can use AA alkalines in and have a USB output. I don't have one but have seen them on Amazon.
For the EC, I took one of these converters for charging USB devices from a Dewalt lithium tool battery, which would be my iphone and inReach. I found I could keep my iphone 6 charged for about a week of normal everyday use from my 18volt battery. I already had the battery and the device seems useful for other than on boats. Overall, kind of bulky for a kayak. http://www.amazon.com/PoweriSite-USB-Charger-DeWalt-Batteries/dp/B00MBU8Z0Y/ref=sr_1_1?ie=UTF8&qid=1426977967&sr=8-1&keywords=powerisite