Has there been a lot of defective backup batteries lately? I am on my second failed battery since last June. Batteries initially seems OK and passes test but then will slowly stop charging and finally die. Acts like one or more of the LI batteries quits taking a charge. Doesn't seem to act as if the problem is in the SV1000. At nearly $200 each I don't want to purchase another if it will only last a few months. :-/