The amount of panels needed will break the bank!!!! Solar panels are based on their peak power production, measured in watts. The 12 volt batteries are often measured in terms of "amp hours."The formula is: Watts = Volts x Amps
So if we make a bunch of simplifying assumptions, a 12 volt, 90 amp hour battery requires 1,080 watts (or watt-hours, to be correct) of solar power to fully charge. A 85 watt panel could do the job in 12 hours, assuming optimal light and various other things that are never all true in the real world. But if you assume 3 hours of good light per day (that's very conservative in the Sierra Nevada mountains), the battery will be back to normal in 4 days. Your best bet is StaynCharge system as this is what a lot of Pros use, I sold them years ago until I became dealer for Procharger. and it uses existing wiring and charges from your tow vehicle.
Stay'NCharge Does not have to replace your AC charging unit. The AC charging unit keeps your batteries charged at very low levels while the boat is in long term storage. However once you switch it to full charge the AC charger will only charge your battery or batteries approximately 80% to 93% percent over a very, very long period of time. That is where the Stay'NCharge system comes in. The Stay'NCharge System will bring the battery or batteries up to a full charge while you drive to your destination. It will even charge your batteries while the vehicle idles. It only takes 22 minutes to bring 1 dead batteries up to a 98% charge!
One 12 volt start battery will charge in 21 minutes & 45 seconds. Three deep cell 12 volt batteries, set up as a 36 volt system (in parallel), will charge up to 98% of capacity in 2 hours 10 minutes and 15 seconds. Try that with your AC charger!
Use the Stay'NCharge system to put a full charge in your batteries and use the AC charging unit to keep your batteries charged at maintenance levels while the boat is in long term storage. Then you will never be disappointed by finding your batteries are flat or very low AFTER you get to that favorite fishing hole.
If you want to extend the life of your batteries you should start charging the batteries as soon as you finish using them and do it with a quick charge. That means as soon as the boat is loaded onto the trailer plug in Stay'NCharge and start extending the life of your batteries. By doing this your Boats batteries should last as long as your car or truck batteries.
The alternator will only feed the amps required by the batteries to charge. This is the same principal that truck and car manufacturers have used for many years. Don't take my word for it, check this out with your local area battery distributor's technical department. As soon as your done fishing and load the boat back onto the trailer you hook up the Stay'NCharge Charge system and start recharging your batteries while driving home or to your next fishing spot. This means you will never have to climb in and out of your boat again while it is on the trailer to hook up your charging system.