A friend asked me to advise which rechargeable batteries I recommend to power on-camera flashes. Wedding photography can be very demanding on a flash unit. Even when a flash is used at low power, it can use up a lot of energy over the course of a wedding day. And when bounced against walls and ceilings, a flash will drain a battery even faster.
I have been using Maha Powerex batteries for years, and currently use Maha Powerex 2700 batteries available from http://www.thomas-distributing.com.
Powerex batteries have served me very well. They put out a lot of power, recycle quickly and last for many recharges. It’s a good idea to write the month and year on them with a permanent marker so that you always know how old they are.
Powerex 2700′s should be charged one or two days before a wedding as they gradually lose some of their charge each day. The same manufacturer offers Maha Imedion batteries which can hold most of their charge for months, but I don’t think those are made for the intensive output and fast recycling that we need for weddings.
I recharge the batteries using a Powerex charger (Model # MH-C801D) that allows for soft recharging. Soft recharging takes longer but is easier on the batteries and lets them last longer. The charger also allows for fast recharging when you’re in a hurry!