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Unplugging battery to prevent drain? / battery recharging and maintenance tips?

I have a '97 Mazda Miata that I have retired from “commuting service” and only drive about once a week, for about 5 miles. I have noticed that the battery dies quite often and find myself having to use a booster pack to jump start it.

Would unplugging the battery when I’m not planning to drive the car help prevent power drain? If so, would I have to unplug both terminals, or would unplugging just the positive one do?

To the best of my knowledge, there is only one active drain on the battery: a factory-installed anti-theft LED blinker that I can’t seem to turn off, even though the anti-theft system no longer works.

What are some other practices for preventing battery drain/properly maintaining a charge, short of daily driving?


Consider the age of the battery. If it 3 to 4 years old, get a new one, that is about they normally last.
The flashing LED will not drain a battery in that short of time. If you want, cut the wires on it.

Don’t mess with the positive terminal at all. Just disconnect the negative and the battery will stay charged. Disconnecting is the only way to keep the battery going without a lot of effort.

You may want to consider a battery tender. A master kill switch located on the batt is another option. If you just disconnect, do the neg thermal. Some products to consider

The palce for Miata info:

I use a Battery Tender rather than disconnecting the battery. The Tender keeps the battery properly charged but won’t overcharge it. There’s one hooked up to the battery of my summer car right now.

You really should drive more than 5 miles if your starting the engine. The engine and drivetrain need to warm up completely, and 5 miles isn’t enough time. Five miles won’t recharge the battery, either.

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Even a reasonable trip once a week is plenty to keep a battery in good condition assuming the battery is good, the charging system is good and there is not abnormal dark load (the power used to keep things like the clock going).  If you need more consider a battery tender or a solar recharger.  If you really must disconnect the battery often, get a switch made for that use.

Once a week should be enough to keep your battery charged. You should get your battery tested for free at your local auto parts store.

If your battery is fine, I recommend a battery tender.

If you really want to do this, don’t disconnect the terminals. too much work disconnecting and reconnecting. As mentioned, a “kill switch”, a switch put on the negative cable to open the circuit.

You are probably right about the alarm system being the problem. You could have a shop the specializes in alarm installations properly disconnect it and eliminate the drain. or, as others have suggested, install a switch in one of the battery cables.

This is the one I was thinking of. If you can disconnect a batt terminal, you can install one of these. Have you thought about the hassle of resetting the clock and radio stations ever time you power down?

More important than loosing the clock and radio settings, a '97 is an OBD II engine computer. I expect that it will loose its memory when you disconnect the battery, and have to ‘relearn’ its normal parameters every time you restart the car. Since most cars require several start/warmup cycles to get dialed in, the system will never be quite dialed in.

5 miles, a restart, and 5 miles home is not enough to charge your battery. That is probably why it is going dead. If it has gone dead several times, you are going to need a new battery, as maintenance free batteries won’t tolerate deep cycling very many times.

Some sort of battery tender would seem to be the best solution. If you park outside. a solar cell unit like they put on RVs while they are parked would be a good choice.

I have seen the idle re-learn mess on OBD1 cars,the idle is all over the map for up to 20 min. it seems. My experience is it is not so severe for OBD2 cars. Maybe some one can comment on throttle and transmission adaptive value re-learns,I would have to look it up and it is probably not the same for all cars.

The LED is probably drawing only 20 mA. You could have some parasitic loss that is not normal. I would check that out. If that is normal, and the battery tests good, get a battery maintainer if you can plug one in. As others have written, 5 miles every week is going to do more harm than good. Take it out every month for 25 miles instead.

I would not want to be having my OBD II car relearning all the time so unhooking the battery would not be my favored solution. One other comment/question. Don’t Miatas have a relatively specialized AGM recombinant battery located in the trunk? If so, not everyone is going to have a replacement.

Yes, The OEM batt is a AGM type. The Westco is the hot aftermarket unit. I have a replacement Mazda batt the is a sealed wet type with the vent tubes for exiting gases out side the trunk.