Security Alarm Backup Battery

I have a problem with our monitored alarm system backup battery. The system itself is 13 yrs old and has never given me any problems untill now. The security company rang me to let me know that the re-chargable backup battery power was showing a low reading. So the next day I went out and got another battery of the same type. I took the old one and made sure the new one was the same. I put the new battery in the system and then a few days later I noticed that the alarm pads power light was flashing. It does not usually flash , normally it just stays continually on. So I rang the security firm and asked what their power reading was and they said it was still low. So then I took the battery back to where I bought it for them to test it and they said it was fine , apart from a minor ampage drop and probably that the alarm systems re-charging unit may be faulty. They said that the battery did need a re-charge. So back to the security firm to see what can be done. They said that they could send a technician out for $120 for the first 1/2 hour and $30 for every 15 minutes after that + parts and materials !!!!!!!!!!!!!!!!!!!!!!
Does anyone here have experience with this sort of thing or know anywhere I can get to have a look at it for a reasonable cost in the Logan City area ?. I am on a Disability pension and really wasn't banking on something to cost that much.
Neil.