Battery Type for Solar Powered Car Stereo

..I can currently get a couple of days worth of use +/- from a 750-900ah battery.

12V(?) 750Ah is a large battery array. Do you perhaps mean a standard lead acid car battery with a cold cranking rating of 750-900A (and a corresponding Ah rating of say 1/20th of that)? Have a close look at the car battery label and its data sheet as the actual Ah rating is not always marked on the battery.

We really need to know your current draw and accurate Ah rating to be able to suggest a solution (and battery size), standard sealed lead acid batteries would be fine but more information is needed to advise what amount of Ah you should have. Is this a fixed or mobile application?

What should I be doing to maintain a battery that have been drained, or nearly drained?

Recharging it! Leaving a discharged vented lead acid or sealed lead acid battery for long periods of time reduces the life of the battery (due to damaging chemical reactions).

Don't forget to have a look on CR4 as this topic has been covered on other previous threads and there is plenty of information and links to helpful battery knowledge websites.

Thanks.. and yes.. it's not Ah.. simply 750-900cca..

Here is a pretty good tutorial on batteries that I found.

(Part 1)(Part 2)

Try a pair of 6V "golf cart" batteries in series. I think they are around 100Ah and will give a true deep cycle. They're not too expensive either.

You are going to be using 2-4 amps/hour running you system, so a U-1 type deep-cycle battery will give you 32ah's, or 16 to 8 hours of run time on your stereo. Your BIG car battery is designed for starting your car; i.e. throwing a lot of amps out over a start cycle period of seconds, and occasionally supplement the alternator when large accessories are running simultaneously. A deep cycle is designed for slow discharge over a long time period.

You don't mention how many hours a day you spend listening to your set-up, but if you are drawing 40 watts out of the batteries and your charger is only capable of a maximum, as in "ideal" of 45 watts, then your solar system is undersized by half of what you need to charge under less than ideal conditions. And you will want to charge the batteries with a voltage around 14vdc. I wouldn't use sealed deep-cycle batteries as they require a special charger that cycles the charge on and off to allow gasses to dissipate.

The volume is never more than about half way up, but It is listened to 3-8 hours a day 3-5 days a week? more/less..

The Kramer 903 amp that I want to use is actually less power hungry than I stated.

..the fan load is maybe up to 500ma? The lighting is less than that.. ..I'm guessing

lots of great site links.. Thanks guys! more reading!

...I just found this passionate review for this amp.