These are the voicechat battery convars available for tuning. They take effect when a new round starts.
Quote
ttt_voice_drain (def. 0):
Enables the voicechat battery feature. Voicechatting reduces a battery meter, when it's empty the player can't voicechat and must wait a few seconds for it to recharge.
ttt_voice_drain_normal (def. 0.2):
Battery drain per tick of voicechat for non-admin players.
ttt_voice_drain_admin (def. 0.05):
Battery drain per tick of voicechat for admins. Set to 0 to allow infinite mic usage.
ttt_voice_drain_recharge (def. 0.05):
Battery recharge rate per tick of not voicechatting.