Hi! I built the schematic from the link below and I wanted to ask if the schematic is compatible with gel accumulators (6V/4Ah) ?
Also does the schematic is compatible with 4.8V 1.2Ah Ni-mh AA accumulators ? (by modifying R4 to 10 ohms).
I have a 12V/10W solar panel and I wanted to charge the battery during day and during night to light up some led's.

https://www.electroschematics.com/dual-mode-battery-charger/

 

Did you miss this line in the description?

for use with a 6V sealed lead-acid battery

 

The article says SLA batteries. I would be cautious about using it on ANY other battery types especially any with the word lithium in the name. It may require some changes to be used with other battery types. I am not that familiar with Ni-mh battery technology and can barely remember reading about gel cells. IIRC lithium batteries can react VIOLENTLY to overcharging.

You would be doing yourself a favor to conduct some research at:
https://batteryuniversity.com/

Please don't enter the competition for a Darwin Award
https://darwinawards.com/darwin/

 

Like what Papabravo said. Personally I would use a chip or charger specifically for type of battery I intend to charge. There are many details that need to be taken care of in order to charge some batteries safely.

https://www.es.co.th/detail.asp?Prod=003514998

 

Gel lead-acid batteries charge the same as VRLA lead-acid batteries.
Nickel based batteries should be charged with a constant current and the charge terminated when they start to heat up, or when the terminal voltage stops increasing and starts to decrease. Full details at Battery University. like @Papabravo says.

Lithium based batteries should be charged very carefully indeed!

 

Four AA Ni-MH rechargeable battery cells are over-charged if they are charged to 6V (1.5V each). Then they will not last long.
Battery datasheets show charging at a low current and 1.35V per cell (5.4V for four cells).
The charger circuit should detect the sharp rise in voltage when the battery is fully charged then it must turn off the charging.

 

Four AA Ni-MH rechargeable battery cells are over-charged if they are charged to 6V (1.5V each). Then they will not last long.
Battery datasheets show charging at a low current and 1.35V per cell (5.4V for four cells).
The charger circuit should detect the sharp rise in voltage when the battery is fully charged then it must turn off the charging.

The voltage falls when it reaches full charge, although the effect is not as distinct as in Nickel Cadmium - see https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride and https://batteryuniversity.com/article/bu-407-charging-nickel-cadmium

 

The voltage falls when it reaches full charge, although the effect is not as distinct as in Nickel Cadmium - see https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride and https://batteryuniversity.com/article/bu-407-charging-nickel-cadmium

I think the voltage falls when the Ni-MH cell is overcharged which should be avoided. It is closer to a full charge during the voltage peak like in the manual from Energizer Battery company: