Introduction: 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 yea…

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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