You don't like your truck? Leaving anything charging unattended, especially in the cold or hot like your truck, is only an accident waiting to happen. I would only use an AC adapter and plug it in at your house to charge. Do not put it on to charge and then go to bed leaving it alone. Since you leave it charging in your truck it could be that it's not getting a full charge, your charger isn't working right, or it could be you have a bad mod. Batteries really shouldn't be left in any kind of extreme temperature condition.
What wattage are you using it? If you're using it at 50W, that will also drain the battery faster than if you have it set at 10W. This would also make a different on what resistance the coil in your tank is. I'm a mouth to lung vaper and like a cooler vape so I use a 1.8 ohm coil. With this resistance, I only use 7.8W - 8.4W (as the coil gets used the resistance goes up slightly therefore I need more power as it gets older). With this low wattage I only need to charge my battery once a week - I rotate between two and three tank/battery units. Does that make sense?
We stress getting back up around here. Once you get the back ups, get back ups of your back ups. Then, get back ups for those. You can never have too many. I've gone through four back ups of battery, tank, coil... in one instance due to various reasons -- nearly all of us have at some point. When that happens, you'll be glad you listened and got the back ups or you'll wind up going, "They said to get back ups and I wish now that I did..." We see this all the time.