Does it matter order of battery disconnection in a car?

[lituya1617]

Car electrical systems these days have computers that stay connected all the time. There is always a small current drain because of the computer draw, about one ampere. One ampere is sufficient to cause a spark. A spark could easily ignite the hydrogen gas that may be given off by a battery; however, a battery usually only gives off this gas when being charged. It dissipates very rapidly and does not "hang around" the battery caps very long. Still, hydrogen gas is very explosive and it will blow your battery to pieces and splatter you with hot acid if you ignite it. Dangerous. Accordingly, you should ventilate the area around the battery before removing any connections on it - just waving a rag over the battery ten times will get rid of any gas outside the battery. Now, you cannot get rid of the gas inside the battery so you still must be careful. Even a small explosion is not a good thing. When disconnecting terminals or checking a battery with a tester it is best to cover the battery with a small sheet of rubber so you do not accidentally cause a short circuit. Always disconnect the negative connection first. The reason for this is that those computers run on 5 volts, not 12 volts. If you touch the frame of the car with the positive lead or a wrench connected to it you will not only get a nice shower of sparks that might cause a gas explosion, the frame forms the negative side of the feed to the computers. It is possible to fry the computers by placing even a transient 12 volt power surge to them as might occur with the negative lead still connected and the positive lead arcing to the frame. Reversing the leads when jump starting the car is a common way that computers get ruined but arcs from the positive terminal can do it too. In summary, be very careful around batteries because they hold a great deal of energy, emit explosive hydrogen gas, and the entire system is designed for the battery to be connected and disconnected in a certain order - take off the negative first.

[pearson 32]

I winter store a 2018 Ford Escape by removing the negative battery cable. The positive post/cable connection is buried under the firewall making cable removal nearly impossible without removing engine components that block the battery preventing room to slide the battery forward to clear the firewall. I chose to leave the positive cable connected. Anyone see an issue with this. I am gone for 6 months.
RH

[Wotname]

^^ I can't see any issue. Having either pole disconnected leaves the battery open circuit and as the negative pole should always be removed first and refitted last, your method is sound.

[lituya1617]

Pearson32: Because lead-acid batteries are damaged by being allowed to discharge fully and because all such batteries have a small internal electrical drain and will discharge over a few months, it is a really bad idea to leave a battery disconnected when storing a vehicle. Batteries allowed to go completely dead and cold suffer damage and may never be able to be used again. May I suggest that you leave the battery connected in your vehicle and attach a "trickle charger" to it rather than just disconnecting it? I bought a "smart charger" for only $7 and I have used it on my lawn tractor during the winter months. Any of my batteries not in use are on a charger. I have never had a battery go dead! My boat batteries are on a Constavolt system and stay fully charged. I attribute success with batteries this to carefully keeping all my batteries charged and properly filled with distilled water. I have had batteries on my commercial fishing boat that lasted over 15 years. Lawn mower batteries are notorious for only lasting for one season - not the fault of the battery; rather, it is because they die without their internal resistance being overcome with a charger. My lawn tractor has a battery in it that is 16 years old. The thing that kills batteries is a short circuit at the base of the internal plates caused by lead sulfide that precipitates and eventually builds up around the lead plates in the battery - this deposition happens much more rapidly when the battery is allowed to discharge fully. This short quickly drains the battery and may so damage the plates that you get a "dead cell" with high resistance that makes the battery useless. The proper care of batteries will save you a lot of time and aggravation.

[pearson 32]

Originally Posted by lituya1617

Pearson32: Because lead-acid batteries are damaged by being allowed to discharge fully and because all such batteries have a small internal electrical drain and will discharge over a few months, it is a really bad idea to leave a battery disconnected when storing a vehicle. Batteries allowed to go completely dead and cold suffer damage and may never be able to be used again. May I suggest that you leave the battery connected in your vehicle and attach a "trickle charger" to it rather than just disconnecting it? I bought a "smart charger" for only $7 and I have used it on my lawn tractor during the winter months. Any of my batteries not in use are on a charger. I have never had a battery go dead! My boat batteries are on a Constavolt system and stay fully charged. I attribute success with batteries this to carefully keeping all my batteries charged and properly filled with distilled water. I have had batteries on my commercial fishing boat that lasted over 15 years. Lawn mower batteries are notorious for only lasting for one season - not the fault of the battery; rather, it is because they die without their internal resistance being overcome with a charger. My lawn tractor has a battery in it that is 16 years old. The thing that kills batteries is a short circuit at the base of the internal plates caused by lead sulfide that precipitates and eventually builds up around the lead plates in the battery - this deposition happens much more rapidly when the battery is allowed to discharge fully. This short quickly drains the battery and may so damage the plates that you get a "dead cell" with high resistance that makes the battery useless. The proper care of batteries will save you a lot of time and aggravation.

Thank you for the response; however, I Winter store fully charged boat batteries without a trickle charge outdoors in Michigan and come spring after re-connecting them the Diesel engine cranks and fires without issues. I use to haul them down a ladder and store/charge them in my basement until one year I fell from the ladder while carrying them up to the boat. Talking with fellow boaters, I heard that battery manufacturers cold store them to help maintain the charge. I was sold on the idea of leaving them on the boat.
I do trickle charge my Porsche with a ‘smart’ automatic charger to avoid shutting down the computer. Not sure a $7 charger would have the capability of a trickle charge without overcharging. I could be wrong, not sure I would trust it unattended. The Escape is also stored disconnected as I described earlier in a cold garage.
In addition, I store a vehicle for 6 summer months in Florida by simply disconnecting that battery. I did have to boost start that battery, but once it was up and running it maintained a charge. No issues.
The temperature difference over similar storage periods appears to be having the affect you might expect.
RH