I’ve got a APC UPS BE500-AS that’s has been left alone for a few months.
When I wanted to use it, I realized the internal lead acid is already flat, and I cannot charge it up with a lead-acid charger.
I bought a new lead acid battery to replace the internal one. It worked fine for a few days. After that I cannot get it to power on anymore.
I’ve tried the circuit breaker switch on the side and that does not help.