Help! The Polarity Is Reversed On My Battery.

August 20, 2019 2 Comments

reverse battery polarity

Reverse polarity occurs when you jump start your car or when you install new batteries.  Polarity is a result of an “accident,” but the effects can be damaging.Can a 12 Volt Battery Reverse Polarity?

Nowadays, much of the gear that can be bought in the marketplace may be damaged by polarity because of poor design techniques.

The Culprit: Poor Equipment Design

There is an area in design where manufacturers are often at fault.  It’s an ongoing trend in their design.  It seems like 12-volt and 24-volt electronic equipment are more prone to damages.  It is a bit ironic because most equipment is designed with some form of reverse polarity protection.  This is usually in a diode and fuse form.

This is the theory: if reverse polarity occurs, the designed diode will then conduct and short the power supply in order to ground and trigger the fuse to blow up.  This protects your equipment. This should work well if the equipment has been designed properly.

Unfortunately, there is a disturbing amount of 12-volt and 24-volt electronic equipment with this design flaw.  They make the copper traces on the printed circuit board extremely small.  Unfortunately, this then pulls a lot of current through the diode in order to pop the fuse which then vaporizes the printed circuit board power trace.  Once this happens, you will then need to replace the whole board or have it repaired.  In either case, this will require expensive repair.

Can Battery Reverse Polarity?

Can Battery Reverse Polarity?

 Yes, it can, but it can happen only in two ways.  First, if you are filling it up for the first time.  If you use an old type of charger, you can short the terminals.  You could be hooking up the charger backward and end up reverse charging your battery.  You won’t see a spark because the battery actually gains voltage while you charge it.  The short won’t be enough to create a spark

You can also reverse the polarity of a battery after you’ve activated it. This is rare, but it is possible. In order for this to happen, you will need to perform a sequence of errors that would eventually trigger the reverse polarity.

The only way to discharge the battery completely is by failing to notice a dead short that will eventually dissipate the battery charge.  After some time, the battery will be discharged entirely.  But in order to have a negative charge, you will need to hook it up backward and charge it again.  So, the only way for a positive-charged battery to reverse itself is to discharge completely, and then reversed charged.

But Can a 12-volt Battery Reverse Its Polarity?

Yes, it can happen. If the battery cells are out of balance, some cells will discharge before the others.  As it continues to discharge, they will start to reverse polarity.  Now, if there is an external factor that keeps the current from flowing, like for instance, when the batteries are in a series, and then one goes bad, the battery will start reversing polarity on some or all of its cells.  It doesn’t really get that bad in an installation if there are no external errors or mistakes that lead to the reverse charge.

To really keep your battery in tip top condition - you will need a industrial grade professional battery maintainer such as this one from NOCO.



2 Responses


September 25, 2020

Recently working on a boat fitting some new equipment. Engine was not running so battery bank ran down. On starting engine, separate battery bank, the battery bank for the equipment still showed no life and nothing connected to it would turn on. Engine was stopped and battery bank checked. It showed less than a volt across the two 12v batteries connected in series. One battery showed 12.4v across terminals and the second -12.6v across terminals. Once disconnected First battery still showed 12.4v but second showed -5.7v. This battery was replaced and when checked all was normal and when engine started the charging kicked in as normal. Over thirty years working in electrics and never seen this. The system was operational and no changes made to it so the only possibility is partly explained above about the battery starting to deteriorate but the conclusion is wrong. It was serious. Luckily the vessel has a separate battery bank for engine starting. But on a vessel with single set of batteries it would have been serious if it occurred at sea. Also there were no external errors that could have done this. The charging circuit is setup correctly and no changes made prior to this happening.


June 02, 2020

the battery in my 95, civic del sol just reversed itself. the only thing i did was keep it charged with a Battery-Minder charger / desulfater which i’ve been using for years with no problems. i am currently using it on other batteries with no issues….. i tried the Battery-Minder on it one last time and it signaled, “polarity reversed”. i checked the battery with my voltmeter and sure enough, it’s reversed.

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