I just picked up a Helix 5 di/gps. Do any of you guys have a recommendation on what type of battery to get?

Check the specs on it and see how many amps it draws per hour, guesstimate how much time you spend on the water each outing, and buy accordingly.

The Helix 5 uses .615 amps, approximately (7.6 watts) at 12.5 volts. Providing you have a good 7 AH battery and the ambient temperature is 80 deg you should get about 9 hrs of run time before your battery drains to aprox 40% (11.9 volts)
This will all vary some as your battery ages and or the ambient temp drops. For each 10 dregs drop in temp starting at 70 deg f you can expect aprox .1 volt drop.
You can extend run time if you're fishing in low light conditions and have your screen brightness turned down, but in daytime you will usually have it full bright.
I usually run a 14 AH / 12V AMG Deep cycle, aprox $35 from atbatt.com.
This will allow for some fishing if you're out a second day.

Thanks. I have one ordered