In article ,
says...
Sounds like you are talking about them being wired in series, for 12 volt
function. So a single would need to be a 12 volt unit., at 5 amps.
Perhaps such as at http://store.yahoo.com/batterysupplyco/index.html

Actually, an exact replacement would be 12V, 2.7 AH, but
anything equal to or greater than 2.7AH will be fine.
--
Mark

The truth as I perceive it to be.
Your perception may be different.

Triple Z is spam control.