Help making mini UPS System

[Mr_Max]

Hi everyone

I have searched for a DIY mini UPS system to connect to a Router, I found this project (the 2nd link) & decided to build it
https://electronicseverywhere.blogspot.com.eg/2010/12/mini-ups-system.html simple revised version
https://www.scribd.com/doc/48939413/Model-of-MINI-UPS-System#scribd Full version

it's working well so far, but I can't get the battery overcharge protection circuit to work properly, I can't find Transistor SL100
So I have searched for replacements & tried 2N2222 & BC337 but they don't seem to get fully open when the battery voltage reaches 13.5 V
the LED in the protection circuit above barely lights up, I tried to measure the voltage across the zener diode by putting one end of the Voltmeter to ground & the other one to the anode of the diode, it is more than 6 volts, the voltage going from the 2n2222 emitter to the LED is 2.2 volts
so I have to adjust the 10K POT so that the LED has strong light, only then the charging voltage slows down but that affects the next charge, the battery never reaches 13.5 V so I have to adjust the POT nearly to the middle. The only time I accidentally got the 2n2222 to be fully open was when I put the 2 leads of the Voltmeter to the cathode & anode of the zener diode, the LED was so bright but seconds later it has burnt.

Also I noticed that the current output from the 12v zener is too low to drive a router
so I had to use 2 voltage regulators (L7812,7809) to get both 12 & 9 Volts

I wish if you can help modify the circuit so that 2n2222 or bc337 fit in, or if you have better ideas to make the protection circuit work as it should

 

[Nigel Goodwin]

The circuit is EXTREMELY crude and nasty, and unlikely to work well regardless of the transistors you use. To make it work properly it needs redesigning to use comparators or opamps (as comparators) to provide accurate switching points and hysteresis.

 

[Mr_Max]

Thanks a lot for your reply, I know it's far from perfect, I have tried it & it works, when I connected an access point rated 9 V 800 mA, it lasted more than 4 hours on the battery, instant switching when AC is back.
but I wish if the overcharging & undercharging parts of the circuit work as they should. although I don't quiet understand what the SL100 & 2N3055 are actually doing in the original circuit ?!
I'm open for suggestions & ideas to make it better & more accurate, could a (relay - op amps) driven charging circuit do the job ?! & how to do that with minimal modifications to keep it as simple as possible ?!