Battery and charger problems

I have a motorino xmr and my batteries were getting weak...also my charger would make a whining noise intermittently when I first plugged it in, I purchased brand new batteries and installed them...my volt gauge on my bike showed 77.5 volts when I first turned the key which is low and no surprise as I was told they would need a charge...I plugged the bike into the charger and had a shower I checked on it about 45 minutes later and the charger had shut off all ready...I turned the key on and it showed 80.5 volts...so I went to try it and the bike behaved like the batteries were dead so I plugged it in again and the charger only ran for about 5 minutes and shut off and again the volts showed 80 so just played with the lights etc. And sure enuff the volts started dropping. Does this sound like a bad chargeer or a problem with the bike...thanks in advance for your opinion

Sounds like a bad battery

Gday.
If the old batteries are weak but still working, you could test the charger with them. A bad charge will go full after a short time on both new &old batts. The old weak batts should take longer than a bad new batt.
Hope I could help.

AussieRider.