I found this and figured it would be good to carry along on my kayak if my 12 v trolling motor battery rund out. good idea?  the dimensions are only 6 3/8" L x 6 7/8" W x 1/2" H.  

http://www.batterystuff.com/solar-chargers/SP60-12.html

really not going to help you at all. first if you read all the way down you can see it sayes " not for batteries bigger than 30ah. that is a small battery, most deep cycles are way more that that 80+ AH . also it doesn't charge fast enough to notice anything if you battery goes low. It would have to stay on the battery for a long long time, days week maybe to help. We use solor chargers on my families pontoon boats, but they sit on the docks from may till oct. and the solor chargers are solor mats about 12 inches by 30 inches. we only use the boats  every other weekend so they help to maintain the batteries since we do not have power on our docks, they help, but still don't charge fully. also you don't notice anything when running.

It is designed to replace the energy that the battery would loose while sitting.  So if you consider how slowly a battery looses energy while sitting, that is about how fast that solar sell would charge.  

Key word - Maintainer

I agree it will never charge your battery while your out on the water.  I did see someone have it mounted to there pontoon boat a couple of weeks ago.

The solar charge is a great idea for if your boat is going to be sitting for a long time, but not if you use it a lot.  You will need to still plug in a home charger to get the batteries back up to full charged after a long day or weekend.  

The solar panel provides 12V at 1.25W.  The math is Watts = Volts x Amps.  So this panel could provide about .104 Amps.  If you had a 30 Amp / Hour battery it would take 288 hours to charge the battery.  Concidering you only get about 4 hours of direct sun on a solar panel most days it would only take 72 days to charge a 30 Amp /Hour battery.  If you could use it on a 100 Amp / Hour battery it would take only 240 days to charge it.  

Send me a email and I will send you something to try and see if it will help. No cost to you. Merrry Christmas

really not going to help you at all. first if you read all the way down you can see it sayes " not for batteries bigger than 30ah. that is a small battery, most deep cycles are way more that that 80+ AH . also it doesn't charge fast enough to notice anything if you battery goes low. It would have to stay on the battery for a long long time, days week maybe to help. We use solor chargers on my families pontoon boats, but they sit on the docks from may till oct. and the solor chargers are solor mats about 12 inches by 30 inches. we only use the boats  every other weekend so they help to maintain the batteries since we do not have power on our docks, they help, but still don't charge fully. also you don't notice anything when running.

Can you provide a website link to the chargers you use? My pontoon boat only gets used a couple weekends a month during the Summer and it would be nice to have a solar charger to keep the battery fresh.