Approx 20 seconds every 6 months. So every month or 2 need to time check. I shoot with 3 cams, flash, lens, 9 batteries, 6 sets of NiMH AA plus 2 sets of Alkalines (I don't bring charger). etc. It gives you a peace of mind for those 4 consecutive AD periods.
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You should consider having one of those Seal Lead acid battery to replace all those battery. I have 2 DIY batt pack running to the 4.2A SLA batt and it just go and go... no flat battery anymore. I clip it on the Lowepro Lens case and put it on the belt. It works like a charm. DSLR batt... just have to bring one charge in the bag all the time... it is light anyway...
If you don't like the weight, just buy those 1A+ version and keep 2-3 of them. Charge them once and they are ready for a long time.
I use to work with lots of rechargable, due to its age, it is sometime unreliable.
I used to use a lot of flashes for interior work and SLA batt is the answer.
Hope it helps.
Regards,
Hart