I have removed the battery from an old portable dust cleaner. The acid has oozed out, and that is the reason the device does not work anymore. I want to replace the batteries, but their voltage is not indicated.
The only hint I have is the charger output. Is there a univocal way to determine which kind of batteries is meant to recharge (like a phone's 5V charger feeds 3.7V Li-ion batteries)? In that case, the charger is 3.9V and 0.5 VA (better, W).
Edit: Added photo. It was a pack of 2 batteries like the one showing in the picture, with my hand holding it for size comparison. Size is similar to a C battery, but not equal (approximately 4.5 cm height x 2.3 cm diameter - 1.77"x0.91")