Q: Battery constantly drained on 1995 Nissan 300ZX

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Since the car was wrecked over a year ago I have had continual trouble keeping the battery from dying. The car is seldom driven and garage kept, but after about 2-3 weeks the battery dies. The repair shop proved truly incompetent. I found (2) issues that I hoped would solve the problem - 1. loose wiring harness (passenger side headlamp, where the wreck occurred)& 2. sensor for hood not making proper contact, preventing the security system from properly initiating- however both have proven inadequate fixes. Any ideas as to what can be causing the battery to continually die? At my wits end?
(1) Answer
First, verify that you don't have a parasitic drain of more than 30-40 milliamps maximum. Most any car that sits for 2-3 weeks and then is driven for a day and then sits for 2-3 weeks, the Battery will eventually fail. This is called 'deep cycling' a battery. Any battery will lose energy as it sits because it is an electro chemical device. As the electrolite solution sits, it wants to and will stabilize, which means a loss of voltage. . Even a brand new battery that has sat on the shelf for say 6 months will lose its charge, I have experienced this fact many times.
I have 2 suggestions 1) install a battery shut off switch on the negative terminal, so when you park your car, the small but normal drains on the battery from the Computer systems memory requirements, clock and security system will be eliminated. this will help. 2) purchase a Marine Battery which is designed to be deep cycled, and will hold a charge much longer, but is more expensive.