Is the autoreflex T or the autoreflex t3 the better option?
Also: What steps are needed to deal with the battery issue?
The T3 is newer and has a couple of nice improvements on it, but if they both are in good condition, they will give similar results.
@Paul Howell 's suggestion about the batteries works - he is probably referring to Wein cells designed for the purpose.
There are a couple of other approaches to buying adapters and appropriate to those adapters that work together as a solution. One gives relatively short battery life with smaller hearing aid batteries, but the prices of those adapters and batteries are low. The higher priced adapters can be used with more expensive but much longer life silver oxide batteries. I have and have used both.
Some cameras can also be modified by repair technicians to take silver oxide batteries directly. If you should decide to have the cameras serviced, it would be worthwhile to ask about that.
IIRC, both cameras will work fine without batteries if you are prepared to use a separate hand meter and set exposure manually.