6 Volt Lantern Flash Light Battery Conversion

Conversion of the 6 volt lantern type flashlight battery into a rechargable LiFePo4 pack.

Introduction

This tutorial is using EverReady type flashlight pictured below, but it can be applied to just about any other unit. light We are going to replace a stock alkaline 6 volt battery pack with a 6.4 volt LiFePo4 rechargable pack. The benifits of this conversion are longer overall battery life, ability to recharge the battery instead of having to replace it and much lighter weight of the flashlight. The cons are the initial cost of battery cells and reduced running time of the flashlight before requiring a recharge. This tutoiral is designed for DIY with the minimal custom equipment envolved.battery

1

Step 1, Preparation

Materials used:
  • 22 AWG wire
  • 2.5 mm X 5.5 mm barrel type socket
  • 4 x 26650 LiFePo4 battery cells, 3300 mAh capacity*
  • 6.4 volts 2S LiFePo4 battery PCB
  • Lantern type flashlight
  • Fish paper or tape
*Other LiFePo4 batteries may be used, such as 18650. We selected this type because of the capacity. The batteries can be purchase with or without pre-welded tabs, we highly recommend pre-welded tabs for ease of soldering the connections.  
2

Step 2, Preparation

Equipment used:
  • Soldering iron
  • Hot glue gun
  • Capacitive discharge welder*
*Not an easily found household tool.  We use it to weld our own batteries, you can purchase the cells with pre-welded tabs or a complete battery pack.  
3

Step 3, Dissasembly

  1. Unscrew the top plastic ring off the flashlight.
  2. Remove the clear plastic protector.
  3. Remove the bulb assembly.
4

Step 4, Pack Assembly

  • Weld or solder two cells in parallel - positive to positive, negative to negative.
  • Repeat for other two cells
5

Step 5, Pack Assembly, cont.

  • You should now have 2 sets of 2 cells connected in parallel.
  • Connect these sets in series by welding or soldering negative side of one set to the positve side of the other set.
  • You should only make this connection on one side.  Do not connect the cells on the other side or you will short out the pack.
6

Step 6, Pack Assembly, cont.

  • This is what the other side (top) of the battery pack should look like.  Note that there are no connections between cell sets.
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Step 7, Pack Assembly, cont.

  • We used hot glue to hold the cells together, this is optional.  Alternatevly, you could use some tape to wrap around the pack.
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Step 8, Adding Protection Module

  • Next, we add a PCB module to the pack.  The module will prevent the pack from overcharging, undercharging and shorting out.
  • Cut a piece of wire approximately 1/2 of an inch longer than pack height.
  • Strip the insulation off both end.
  • Route the wire through the center of pack to the other side.
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Step 9, Adding Protection, cont.

  • Solder the wire to any tab at the bottom of the pack.

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