One simple solution which cost me zero $$ and few hours of fun:
Pre-requisite - RC Li charger. I had different models already (e.g. IMAX B6), hence the solution was easy. Imax B6 operates from up to 18DC - hence you can use many sources to power it up - e.g. Car on board power or in my case - old IBM laptop PS (18V).
End result: 3-in-1 device: Flash Light + 2xUSB 1A Charger + Battery Power supply for my cordless drill/screwdriver.
Components - all recycled from the old obsolete stuff:
- Dolphin Flash Light without the battery. 4.8v Bulb on board. Used as a body for the project and as a Flash Light in the 3-in-1 end product;
- 10 x Li-Ion 18650 batteries from failed laptop packs. (note: sometimes one pair in the 2P3S pack fails but the rest 2 pairs are good in my case ~ 3.5 Ah/pair remaining capacity) (Note: I have Professional tools to test laptop packs standalone and see what the condition and the remaining capacity is and Professional Battery Capacity Testing tools, but you can use cheap IMAX or other RC chargers to load test the Li capacity with 10% accuracy); Batteries were reassembled into 5P2S configuration - that is 7.2V nominal output (8.2V Max) with 11Ah capacity if new - in my case - about 9Ah left.
- Switch from some toy model - to switch LM7805 off when not in use;
- LM7805 Voltage regulator - fixed 5v @ 1A output - to feed USB and 4.8V original bulb; Got it from some old transformer type network power supply;
- 2 x USB ports taken from the front of an old PC;
- LM35 Temperature sensor (optional and only required if batteries are charged by IMAX charger) - those were a gift from Texas Instruments;
- Few wires ending up with 3 small plugs (power; temp sensor, balance charging) sticking out of the flashlight body - to be able to charge batteries without dismantling the flash light, to quickly test the condition of the batteries inside using one of my portable "baterryless quick test Li probe" (you can use voltmenter instead) and to power “cordless” drill which is 7.2V rated.
One leftover 18650 cell went into the small brother - another flashlight made of broken LED light, another small toy switch and canister from Vitamin C tablets: