I keep seeing everyone recommend a size 27 battery for everything.  Question is why is the 27 much better?  I'm assuming it'll have more capacity for a long day on the water but is there necessarily any more power?  Reason I'm asking is that I have 2 batteries that I use for the 24 volt tm in the bassboat and I always pull the size 24 out to use when I take the jon boat out.  I do it purely for less weight.  The 24 has more than enough power to run me all day but I was just wondering if there was really a difference.

The group 24 batts are good for 75-80 amp hours and the grp 31 are about 100-110 AHs. the grp 27s are in between. No other difference except the size and weight. If the 24s are good enough, they are easier to carry and less expensive. I have used them for years on my light kayak and haven't wore one out yet.

The 27 series with give you about 15-25% more amp hours and reserve capacity than the same battery in a 24 series.

Thanks!  I figured that's all it was but I'm battery illiterate and had to ask.  

If you want to get a first hand look, go to a battery mfg site like exide and look at their battery comparative specs.