Apols. Tinternet is playing up tonight, hence above non posts.
Usually battery companies will give a 'lifetime guarantee', not for us but for the battery. They assume that they will be beaten to death, so it is unlikely that you would be able to make a claim against them. When it dies its over its 'lifetime'.
Batteries on boats are a 'consumable' commoditee and as such will need to be replaced over time. Have to replace my domestics after 6 years soon (wet lead acid open), and think that I have got my monies worth. Look after your batteries and learn how to maintain them which will extend their life and make your 12v experience more pleasureable.
Knowing the electrical layout on Dog House, replace like with like; battery box fittings etc, and you won't go wrong. The likelyhood of getting a refund from a battery company is about as likely as a snowflake surviving in the Sahara.