# New rechargeable batteries, old charger

**URL:** <https://boards.straightdope.com/t/new-rechargeable-batteries-old-charger/767116>\
**Category:** Factual Questions\
**Created:** [September 28, 2016, 1:24pm UTC](https://boards.straightdope.com/t/new-rechargeable-batteries-old-charger/767116 "2016-09-28T13:24:51Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\
**Post date:** [September 28, 2016, 1:24pm UTC](https://boards.straightdope.com/t/new-rechargeable-batteries-old-charger/767116/1 "2016-09-28T13:24:51Z")

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What numbers do I need to look at to tell if it’s safe to use my new Eneloops in an old Energizer charger that I have?

TIA

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**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\
**Post date:** [September 28, 2016, 1:39pm UTC](https://boards.straightdope.com/t/new-rechargeable-batteries-old-charger/767116/2 "2016-09-28T13:39:09Z")

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You need to look at the battery chemistry. The new batteries are likely NiMH (nickel metal hydride) where older rechargeables were often NiCD (nickel cadmium, aka ni-cads). A NiCD charger usually won’t charge a NiMH battery properly.

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**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\
**Post date:** [September 28, 2016, 1:40pm UTC](https://boards.straightdope.com/t/new-rechargeable-batteries-old-charger/767116/3 "2016-09-28T13:40:31Z")

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If the old charger has an NiMh setting, it’s OK for the Eneloops.  
If it’s NiCd-only, don’t use it.

If it’s a simple trickle charger, you can charge the Eneloops with it, but don’t keep them on the charger past 14 hours or so.

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<div class="post-metadata">

**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\
**Post date:** [September 28, 2016, 2:16pm UTC](https://boards.straightdope.com/t/new-rechargeable-batteries-old-charger/767116/4 "2016-09-28T14:16:57Z")

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It both has a switch for NiCD-NiMH and is a trickle charger, so this is all good info.

Thanks again!