How do you deal with your 5th battery? My charger is such that I can only charge in 2s or 4s. So if I decide to use the 5th battery, one of my battery is not being used. Let say I repeat this process 1000 times, and I happen to not use one particular battery. On my 1001 time, I use the 6th battery that hasn't been used at all. I would think that this battery would hold more power than other 4 batteries. Would this hurt SB800? What about when the 5th battery is significantly weaker/older than other 4? So far I have not used my external battery pack but I want to start using it. I missed few shots at a wedding last weekend due to slow charging flash. Another question, when using 5 batteries does it last longer or is all of extra power used to speed up the charging time?