DIY Rechargeable Lantern LED Flashlight Conversion




About: Professionally, I'm an IT Engineer (Executive Level) and Electronics Tech. I'm a Amateur Radio Operator (KK4HFJ). I lived off grid, with Solar (PV), Wind, and veggie oil fueled diesel generator power for 6 y...

I wanted a good rechargeable LED flashlight, that would combine long battery life, and a very bright output. I could have bought one, but where is the fun in that?

UPDATE! Most Store bought LED Flashlights do not work well with rechargeable batteries, as the typical rechargeable (NiCd / NiMH) is 1.2v instead of 1.5v, causing dim lighting even when fully charged. This Project uses a constant brightness bulb, so no dimming. When battery voltage drops too low, light goes out.

I started with a $3 lantern flashlight from Walmart, installed a 1 watt replacement LED, a 4 D cell carrier, and 4 NiMH 10ah batteries. I have gone a full year of regular use, and just swapped the batteries for another charged set, and put the old batteries in the charger for next year.

Here is the original post -

Lantern Flashlight - $7
1 Watt LED replacement bulb (constant brightness) - $16 (never have to change this)
4 D Cell Adapter - $3.50 (Walmart -

10ah NiMh D Cell (x4) - $5.20 each

Tenergy Advanced Universal Charger TN190-4 Channel AA/AAA/C/D/9V Ni-MH Charger with LCD Display and USB Power Outlet - $30 (smart charger, solar and auto ready)

Step 1: Lantern Body

Pretty much any 6v Lantern Flashlight will work. From the Cheap $3 units from walmart, up to the heavier and more durable $10-$15 units From Eveready and Rayovac.

There's no prep work, except to remove the battery if it's installed, and the existing light bulb. Keep any small parts that hold the bulb in place.

Step 2: The LED

The unit we have chosen is a multi voltage 1 watt LED, which is voltage and current regulated, so Brightness does not change until the batteries are completely empty, then it flickers out. Turning the light off allows a bit of recovery on the battery, so you can use it for brief periods while looking for your back up set of batteries. Remove the existing light bulb, insert the new LED, and prepare for battery install.

Step 3: Battery Adapter

This adapter allows you to replace the one time use 6v lantern battery with 4 D cells. It's a simple direct fit and replacement. No mods necessary. Battery orientation is stamped on the adapter.

Step 4: 10 Ah D Cell NiMH

These are very high capacity (10ah) rechargeable (NiMH) D cells. They have no memory effect, unlike the NiCd versions. You can use any D cell you wish, but performance will vary. Battery orientation is listed on the adapter.

Step 5: Charging

We use a multi battery / multi format smart charger. It stops charging when the individual battery is full, so the batteries do not wear prematurely. It has a 12v input, so it's solar and auto compatible. It charges many formats, from AAA to 9v, including a USB charge port for cell phones, etc.

Step 6: Conclusion

I could have purchased a completed flashlight, and maybe for less, but would not have been able to get the features and flexibility I wanted, nor the fun of creating something. This flashlight is now a year old, and I'm very happy!



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    8 Discussions


    3 years ago

    I have tried to find a regular led bulb that is not + or - directional, with no luck. I settled for an hp 74 lumen, "nite ize" led bulb. I also had to modify the D cell adapter, with very small brass screws, threaded, then solder'ed, into the negative side contacts to elevate the battery contact 1/8" above the negative side platform base. NOTE!..slightly reaming the retainer contact studs, ( i used a very small phillips screw driver ) will help start the brass screws. This step was necessary, because the adapter had plastic "rails" to support the positive side of the batteries, on either side of the positive contact plate, making the simple task of installing the batteries in backwards, useless. After completion, the center spring contact on the adapter's top, is now positive, making the use of a cheaper led bulb possible. note! I used a heat sink when I did the soldering, because the D cell adapters from "rayovac" are made from abs plastic. Walmart stopped carrying the adapters, was "out of stock", as I'm converting two lanterns, I found two on ebay for $8.99 w/free shipping. 5/15/2016

    Thanks for the inspiration Steve!

    Denis Kinsner

    3 replies

    Reply 3 years ago

    LED's by definition are directional, they are diodes. A bridge rectifier can make them polarity insensitive, and no matter what polarity is presented to the bridge, + always comes out the same pin, and - out the other.


    Reply 3 years ago

    Hi Steve. Thanks for the electronics description! I'm a complete novice at these kinds of things. Was the more expensive LED you used in the floating lantern project, equipped with a bridge internally? Your instructions show the LED just being "dropped in" My solution allows the use of any LED bulb to be used, that's the only reason I posted it. Versatility, cost and availability. To me, reading spec's on expensive LED's is like reading Greek.


    Reply 3 years ago

    I've never run across a reversed polarity flashlight, so I don't know if this unit takes that into consideration. It works just fine in the scenario outlined in the instructable.


    4 years ago on Introduction

    I've come to the conclusion that a lantern with a 6V PR13 incandescent bulb and heavy duty, industrial 6V lantern battery is still best. If you want a whiter, brighter light, longer life and slightly lower current draw, replace the bulb with a KPR13, its inert-gas equivalent.

    My Eveready lantern is 20 years old and on its second battery. I may have replaced the PR13 bulb once. Whenever I need it for a quick inspection in the crawlspace, attic, or dark corner of the garage, it simply works. I don't have to worry about rechargeable batteries having internally shorted out or having self-discharged to the point where a LED bulb no longer lights. Even if the voltage of the battery drops to 4V, the bulb will still produce usable illumination. There's enough space inside to pack a spare bulb or two with a bit of padding. It's an ideal standby light for emergencies.

    1 reply

    Reply 4 years ago on Introduction

    I'm on the same NiMH d cells for 3 years, only recharged once. virtually no self discharge that I have noticed. This bulb is constant brightness even down to 3v.


    5 years ago on Step 5

    why cant i do a copy an search on the first line of text?


    5 years ago on Introduction

    have u been to . they have a u.s. based warehouse to ship many item that your looking 4 to your house.