Crystalyte electric Hub motor unit


I have a Crystalyte 36 volt 25 amp hub motor and batteries. It has been in storage for nearly a year although I was assured that the batteries were kept charged. When I had it initially I could get 12 to 15 mph on a mild grade. Now it is doing good to get 5 mph and maybe 8mph on a level stretch. I had a little digital voltmeter that would read 39volts after a full charge .,After I got it back it would only read 37. My regular multimeter does not read amperage , only voltage and resistance .I am looking for meter that will read actual amperage and not idiot lights, but doesn’t cost a fortune .I want to check first before I consider buying new batteries. Any suggestions ?