(12-10-2014, 02:26 PM)justMongo Wrote: I think I need to go to a Marine battery.
The "marine" deep cycle lead-acid 12 volt batteries are all I use in my two vehicles now. They are heavy duty with more lead and the lifespan is much longer than standard auto batteries. They're aren't "true" deep cycle, but rather a hybrid mix of standard and deep cycle, and therefore don't cost much more than $80-100 or so. Look for the ones with an amp-hour rating of 100 or more. If they have no amp-hour rating on the battery, they're probably cheap junk. The CCA (cold cranking amps) doesn't mean a whole lot except to judge how many amps the battery can deliver in a few seconds time to crank the engine.
In deep cycles, the amp-hour rating is what counts. An additional benefit is that if you keep the marine battery in relatively good condition, after it's normal 3-4 year lifespan, you can keep in your garage, charge it every other month or so, and use it to run your CPAP machine in emergencies. I use a "BatteryMinder Charger/Maintainer/Desulfator System
" (about $50 on Amazon) to keep mine topped off and for desulfation. It's a trickle charger with an automatic desulfation mode.
My dad keeps one attached to his auto battery just about all the time the car is stored in the garage - that system will not harm a battery - but you do need to make sure your water levels are topped off in the battery, as any charging will cause some of the liquid to evaporate and you never want the level to go at or below the "fins" in the battery. Some claim that you can put a dead, sulfated 12 volt batter on one of those BatteryMinders for about week or so and it can come back to life.
A lot of short trips around town will run down a good battery unless you keep it charged up. If a 12 volt lead-acid battery is deep-discharged too many times and is allowed to remain in a discharged state, it can ruin the storage capacity over time. Could be that your alternator is going bad perhaps, (it's responsible for producing electricity and charging the battery while the engine is running). I've heard it's always good on a car in general to get up to highway speeds for several minutes every few days, and that helps with keeping the battery charged up.
Here's one similar to the ones I use in my cars:
For my cheapie solar panel system, I use 2 Trojan (real) 6 volt deep cycles, hooked up in series to make a total of 12 volts, like this: