I run two 16v batteries and put on the charger between rounds. Can't risk a voltage drop off.
There has been a whole lot of discussion concerning V batteries on
http://www.promodzone.com/showthread.php?t=16456 and also
http://www.promodzone.com/showthread.php?t=15815 and also
http://www.promodzone.com/showthread.php?t=11890
These threads orta put you off ever touching a V battery. Worked for me!