I'm going to buy a new battery for the car tomorrow morning. Supposedly my battery life is shortened by my near constant use of the 750-watt inverter and other chase-related things (wxworx, cell phone, chargers, etc) on long trips, according to several mechanics I've talked to over the years.
Dan,
The problem is not likely so much your battery as it is your charging system as a whole. I'm assuming that you normally only use your equipment while your engine is running, or at least most of the time here.
If your electrical load exceeds the current that the alternator is capable of supplying, your battery must supply the extra current when it is demanded. The end result is that your battery is likely being "deep-cycled" somewhat; when the load becomes a bit less the alternator has a chance to charge it back up somewhat. This trend is harmful to normal car batteries... regardless of the quality of the battery.
I understand that you don't want to mess around with an aux battery, which doesn't really address this issue anyways... but here are some other solutions:
1. The best solution is to upgrade your alternator to something that can supply the current you need. Keep in mind that this will not help you if you drain the battery while the engine is off. High-output alternators are available for most vehicles, or exisiting alternators can be upgraded in some cases. Most Emergency vehicles have high-output alternators installed (to my knowledge).
2. Many people have found the Optima yellow-top AGM cells to be a good solution for this. They can be deep-cycled, but unlike the normal marine/RV deep cycle batteries they also provide decent starting current. A lot more expensive than regular batteries, but possibly cheaper than the upgraded alternator route. Walmart carries the optima brand, but I'm unsure if they have this model (must be the yellow top version). Lot's of car-audio enthusiasts go with this option. Keep in mind that this option will not help you start your car if the battery didn't get much of a chance to charge back up.. but it sounds like you've been managing okay from that perspective. I'll echo David's comments here... when something is wrong it's nice to have quick access to the parts/warranty.
Of course I'm basing all of this on some assumptions. In my case I also have an aux battery, but only because I have some high-current needs when my engine is off.. and I like to be able to start my jeep afterwards..
Hope this helps.
