Camping light .. 10 watt fluorescent lamp
Was bored yesterday... found an old 'emergency exit' lamp among the flotsam in the spare room. These lights are fitted above doorways and switch from mains power to battery power in case of power failure.
Dismantled it, and tested the 2 D cell nicad cells. Dead as mutton. Flashed 12 volts across them several times for a one second duration from a battery charger, and re-tested them.... 2.1 volts! Did the same for another old pair of batteries. Same result!
Paralleled the two banks of batteries inside the fitting. Fitted a power cord to the fitting, and plugged it in.
One fluorescent immediately lit up, and the batteries indicated that they were charging.
Tested an hour later by unplugging from the power, and the other fluorescent immediately lit up, altho it faded out within a few minutes.
Proved that the charging circuit was working, so I removed the 'mains operated' circuitry and lamp, and plugged it in again to fully charge the batteries overnight.
Today I unplugged the unit at 1 pm, and the lamp is still operating over 8 hours later! (normally, with only two batteries, they only last around 4 to 5 hours max) All I have to do now is fit a battery isolating switch to enable me to switch on and off as needed, and I will have a u-bewt fluorescent camping light that can run for 8 hours or more continuously (or over several days with a couple hours use each day) between charges!
Might glue some alfoil to the body as a reflector, as the plastic body is fairly grungy with age.

... and just made from junk! And it easily fits into my top box.