When I got them fresh out the box they worked great. But when their batteries ran out it was too exhausting to recharge the batteries manually. And after a couple of years, it was almost impossible recharge the batteries because they were too old. Now, a hefty 5 minutes of cranking produces only 20 seconds of light.
I decided to mod one of the flashlights by switching the lithium ion rechargeable battery with a super capacitor.
Surprisingly, the mod was easy and the results were very satisfying. Now, with just a mere 5 seconds of cranking I get 5 minutes of light. A major improvement.
In a further mod I added a joule thief which increased brightness (see step 5)
Step 1: The Back Up Super Capacitor
The neat thing about super capacitors is that they last much longer than rechargeable batteries. They are easier to recharge because they have almost 100% efficient while the batteries lose between 50% to 30% of the energy when recharging.
I am using a 1 Farad super capacitor. But you can use bigger values. The bigger the super capacitor the longer the flashlight works.
Step 2: Replacing the Old Battery
The only thing one has to worry about in this step is to get the positive of the capacitor in the same hole as the positive side of the battery. The same thing with the negative side.
Step 4: Reverse Engineering the Hand Cranked Circuit
The pictures below show the different steps in reverse engineering the circuit.