Our 1991 P42 came equipped with two wet 8Ds having a total capacity of 480 amp hours. With a full charge we have consumed about 240 amp hours when the battery level drops to around 12.1 volts. We spent many days on the hook during our cruises over the years. Our life style (I run seven miles every other day) requires that we run the Genset for two hours every other day. This gives us hot water for bathing and cleaning plus it tops off the house and starter banks. Even though a solar panel or wind generator might extend the charge cycle beyond every other day, we still would need to heat water for bathing. Of course there are other alternatives, but since the sun never shines in the NW (ha ha), the Genset works great for that and running it for a couple of hours every other day is no big deal. In the morning, if the hot water tank cannot deliver hot enough water for shaving and wash up I will boil water on the stove. So, for us the standard battery configuration with Genset works great for our needs. As I mentioned earlier, if our ah needs increased over time, I will add solar panels and/or wind generator before I add ah storage capacity. Ive not checked on this but perhaps 8D gel or AGM might give you more ah than wet, assuming that you can get them in 8D. Lots of choices.

Update 11/2014: A few years ago we retired our end-of-life wet 8Ds with AGM 8Ds. Same ah capacity as the wets, but have noticed some difference. First, no need to add distilled water every two months. Also, it seems the AGMs will absorb ah at a greater rate than the wets. At least according to what our Link 1000 displays. Replacing all of our incandescent bulbs with LEDs has helped reduce the DC load requirement over time.

Updated 11/2014