EN-EL3, EN-LE3a, and EN-EL3e
Nikon's EN-EL3 family batteries are widely used among Nikon's popular mid-range
digital single-lens reflex (DSLR) cameras, such as the D70, D80, D200, and D300.
However, over time, Nikon has introduced three different versions of that battery:
the original EN-EL3, the EN-EL3a, and the current EN-EL3e.
Unfortunately, they are not completely interchangable.
All three versions are 7.4 volts and have the same external dimension.
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The original EN-EL3 was introduced back in February 2002 along with the D100 DSLR.
It is rated at 1400 mAh and is black in color.
When Nikon introduced the D70 in 2004 and the D50 in 2005,
they continued to ship the EN-EL3 with those DSLRs.
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At the same time Nikon introduced the D50 in April 2005, they also slightly updated the D70 to a newer D70s,
but Nikon included a new battery the newer EN-EL3a with the D70s. The EN-EL3a is rated at 1500 mAh,
instead of 1400 for the original EN-EL3. Otherwise, the two versions are completely interchangable.
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Later on in 2005, Nikon introduced a new higher-end DSLR the D200 in November.
The D200 requires a new EN-EL3e battery.
This version of the battery has one more electronic contact and a deeper groove.
It is also rated at 1500 mAh but is gray in color
so that it is easy to tell it apart from the older versions.
The D80 introduced in August 2006 and the D300 introduced in August 2007 also require the EN-EL3e.
The battery compartments in the D80, D200, and D300 are designed such that
if one tries to insert an earlier EN-EL3 or EN-EL3a without the deeper groove,
it would be blocked and one cannot close the little battery compartment door.
However, the latest EN-EL3e can be used on all DLSR models, new and old, mentioned above.
The MH-18 Charger

There are also two versions of the corresponding charger, the MH-18 and MH-18a.
The MH-18a is slightly smaller. All versions of the EN-EL3 batteries can be charged on either charger.
Both chargers are dual ranged, compatible with 100V to 240V AC.
As long as there is the right style of adapter plug,
one can directly plus an MH-18 into any outlet around the world
without any transformer.