(ET) Battery failure?

[willaim att net]

Hello Group: 
My E12 has started to lose speed and endurance. The batteries are 
old but all measure about 6.1 VDC after use. There are no warm cables or 
terminals. The drive and mower motors don't get hot. The fuel gage goes to 
mid 
red fairly quickly while mowing. It won't go very long in 4th gear. After 
full 
timer charge the gage goes to upper 1/3 of Green. This degrading 
performance is 
over the last 2 weeks. I'm thinking its time for getting new batteries, 
but I'm 
not really sure that's the problem. Any suggestions?

Is there an easy way to make an electrical capacity test on a battery 
using a certain piece of everyday metal, an ampere gage, and stopwatch? I 
seem 
to remember that on a posting way back.

Thanks, Bill Alburty 66206