I started one of these conversion projects a couple weeks ago, wired the garden light's circuit board to a prototype board for testing. playing with various battery and LED configurations, as well as solar panels for recharging the batteries. Other than removing the LED and the photosensor(actually replaced) from the circuit board, I've not made any other changes to the circuit board circuit itself. Pretty sure we're using the same Chinese made $2.99 garden light special. I've actually got several still going into their second winter season in NH. Solar panel is as others described, burnt but still charging the batteries(well, my better replacement battery).
The original circuit had only one 1.2v/480ma real cheap AA battery driving a single diode.
Here's what I've done so far, battery and LED wise.
Single AA, 1.2v/1900ma powering a single 3.3v/25ma(Radio Shack) LED.
Two AA 1.2v/1900ma powering 1, 2, and 3 of said LEDs in series.
Two AAA 1.2v/1000 powering 1, 2, and 3 of said LEDs in series. After 3, the circuit lacks the current needed to drive a 4th LED.
Two AAA 1.2v/1000 powering 1,2,3,4 of said LEDs in parallel.
I have also swapped in a Jumbo 3.5v/20ma LED, also Radio Shack without issues.
Still tinkering around with the right solar panel configurations to recharge which ever battery configuration I'm going to settle on. I know the typical solar recharge requirement is more voltage than the batteries being charged, at no more than 10% of the battery's AMP capacity. So for a single 1.2v/1900ma battery, at least 1.5v, but most "model" panels are at least 3v. Which is what I'm using, 3v/25ma, so theoretically I need 190ma, so I could probably get away with 8 panels in parallel, 200ma. Theory, without knowledge of the limits of that Chinese circuit board.
No worries, all the components will come off and onto the prototype board eventually. It's just two diodes, two resistors, a cap and the NPN, LED already off circuit, as is the photosensor.
More to come