When to change out batteries?

How often do y'all change out your boat batteries? I know of some that change them out every two years. They fish quite a bit (I'd say on the average of six to 10 times a month). Do y'all change them out based on the length that you've had the batteries or based solely on the performance of the batteries. I'm thinking that I'd rather change them out before I start having performance issues. I'm not sure how many hours I have on them but they came with the boat when I bought it new in August 2013. Also, is there a particular brand of battery that y'all seem to have worked well and lasted?

You will get a lot of opinions on brand. I personally have had good luck with the batteries at Batteries Plus. I think its called Bulbs and Batteries now. I've also owned several from Walmart and Academy's Stowaway's with okay results.

IMO I see no need to change them until you start noticing performance dropping off.

Tip: Charge your batteries within 24 hours of discharging them. When you come home charge them! Also, make sure you have a deep cycle charger capable of at least a 20-25 amp charge. You will never get a full charge out of a maintainer trickle charger. Bring them up to full charge and then hook up your maintainer. Never let a discharged battery sit for long periods of time. Keep them charged. I also disconnect my batteries when my boat is in storage.

I get a new one when the battery cannot hold a charge for more than 24 hours. If I charge a battery I check it a day or two after and if it losses 15%-25% of the charge after only 2 days then it is time for a new one. I have gone to the sealed lead acid AGM battery for more time use on the water.