I have 12v Dc rechargeable fan. It used sealed lead acid batteries 2 x 6V 6AH .. I bought replacement batteries which 6V 4.5AH as 6AH are not available in market. Will these work? Furthermore while replacing batteries I did something wrong and now there is no power in circuit even with old batteries. I checked the circuit and made its fuse direct. While checking it directly I also burnt a little circuit. Now only with old batteries I can get the light and fan on for a second or two, but when I connect to electricity there is no power or even when I connect it with new batteries there is also no power.

I have checked that power from batteries is reaching to circuit but not moving forward in circuit properly. Which part should I replace? Please see the picture attached.

 

Its a SUNCA 2608 OR LIDO 2608 Fan.

 

While checking it directly I also burnt a little circuit

Are you going to show/tell us which little circuit?

 

Are you going to show/tell us which little circuit?

Where The print of circuit is broken, I have made a direct connection using white wire.

 

This is purely a guess - but it looks like the damage occurred at U101 (the transistor looking device). If so I'd guess that U101 may have blown out. Judging from the video it would seem that when you power up the circuit, some sort of battery protection device (possibly U101) is not detecting sufficient voltage and is shutting the system down before it can drain your batteries completely, which can lead to premature battery failure. But like I said, this is all just a guess. I have no schematic to look at, no data sheets, no component bill of materials, so that's all I can do. Traces on circuit boards don't just burn out for no reason; something over-currented the circuit - possibly hooking up a battery wrong (reverse polarity). But again, this is just guesswork.

Why have you bypassed the fuse?

There's a lot you need to verify as well. Are you getting low voltage AC to the board? Are the diodes shorted or blown open? Just because voltage is "Reaching" the board does not mean much. If the rectifiers (diodes D107, D106 [and presumably] D105 and D104) are blown (or any one of them) then the circuit will not perform properly. On the other end of the spectrum, if the batteries are not being charged then perhaps the low voltage is the reason why the fan powers on then right back off as in the video. Do you KNOW the batteries are fully charged? IF they're not charged (new or old) they're not going to do much.

But please keep in mind at best all I can do is guess. Hopefully this may send you in the right direction. And please protect your circuit with a fuse. They're there for a reason.