I have a rechargeable desk led lamp with USB power input. Although it's supposed to hold charge, it only works when plugged. I opened it and found that the problem is about included lead acid rechargeable battery.
I cut out the broken battery and connected a li-ion 3.7v in its place that I got from an old broken cellphone.
Lamp lights up just fine now but I'm afraid to connect the lamp to a power source since li ion and lead acid are different type of batteries. Am I creating a potential fire hazard or is it fine?