So I use a 10AH NIMH 12V. I initially thought it was 12AH but I checked it's only 10AH.
I found the exact battery on ebay, but it's gone up slightly in price.
http://www.ebay.com/itm/131018888014
When I bought mine everyone was using the normal lead acid batteries. Some people thought it was stupid or unnecessary to buy a fancy battery, but it was half the size and weight, had a longer power curve and according to the specs it was supposed to last for hundreds, even up to a thousands of charges if properly maintained.
Here's it's size compared to a standard 7AH sealed lead acid battery.
I don't have a thousand trips on it, but I do have a lot, and I think I bought the battery around this time of year back in 2008. It's still good and as a comparison I've gone through three lead acids for my bait tank since I bought it.
I just run electronics, but that's includes chart plotters, squid lights, and an old 300,000 Candlepower Q-Beam I carry for hooping.
I don't know that much about the newer technology batteries like the Lithiums, I'm sure they are great, but I'll tell you if my NIMH died tomorrow I'd buy another one, and right now at this point it wouldn't surprise me at all if I got another two or three years out of this battery.
Just from my experience I'd say buying a better battery definitely pays off in the long run.
Jim