# Battery Green eye

**URL:** <https://community.cartalk.com/t/battery-green-eye/78373>\
**Category:** Maintenance/Repairs\
**Created:** [March 31, 2013, 7:23pm UTC](https://community.cartalk.com/t/battery-green-eye/78373 "2013-03-31T19:23:16Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![cwradio](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@cwradio](https://community.cartalk.com/u/cwradio)\
**Post date:** [March 31, 2013, 7:23pm UTC](https://community.cartalk.com/t/battery-green-eye/78373/1 "2013-03-31T19:23:16Z")

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I have a 2011 CR-V EX (23,000 miles).  
After a 800 mile trip I noticed the built-in hydrometer on my battery was **not showing green**. It was showing dark. So I checked the fluid with a hydrometer and it was OK. I tested the battery with a digital volt meter and it read 12.66 volts, again OK. I brought it to an auto parts store and they tested the battery with a load, again OK.  
My question why is the built-in hydrometer not showing green?

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**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\
**Post date:** [March 31, 2013, 7:30pm UTC](https://community.cartalk.com/t/battery-green-eye/78373/2 "2013-03-31T19:30:42Z")

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If you have an hydrometer and know how to use it ignore the green eye. It’s a sales gimmick. You could shoot a hole in the 5 cells and the green eye would still indicate that the battery was good to go. How useful is that?

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**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\
**Post date:** [March 31, 2013, 8:48pm UTC](https://community.cartalk.com/t/battery-green-eye/78373/3 "2013-03-31T20:48:23Z")

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I agree with Rod Knox that it’s a sales gimmick and that it’s also not accurate. The prior AC Delco battery in my oldest son’s car showed a green eye and it was so weak that it wouldn’t even start a lawn tractor or hold a charge for half a day.

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**Author:** ![SteveF](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/stevef/32/2_2.png) [@SteveF](https://community.cartalk.com/u/SteveF)\
**Post date:** [March 31, 2013, 9:39pm UTC](https://community.cartalk.com/t/battery-green-eye/78373/4 "2013-03-31T21:39:45Z")

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The green eye of a car’s battery is not a hydrometer, as many people assume. It merely indicates the level of the electrolyte. It works by the principle of light refraction. A dark eye indicates a low level of electrolyte.

This gimmick might be useful for batteries in which you can add electrolyte. It serves no purpose on maintenance-free batteries.

Note that a battery with a dark eye might still be perfectly OK, and that a battery with ample but weak electrolyte will still show a green eye.